Mark, nice looking plan, I think Lew is on the right path. If you use a support a 1/4" taller would give you a 1/2" clearance then you could use anything you wanted for road bed. Even if you just used a thin steel plate as it is the bottom clearance would be the same as you have now.
If you go with both a 1/4" along with a thin product you will be golden! If you need I have some used I think its 1/8th or 1/4" plexi glass I could cut your curve into with no problem.
Either way its looking good!
Thank you Andy, Marty, Mike. I was fiddling with it last evening some. I do think I will use some thinner, sturdy material for the crossover above. I may just glue the cork roadbed to that material and forego the Homasote at that point. I won't be using Homasote on the bridges that will be at the raise up access point a few feet away either. Mike, the thinner material doesn't even have to be cut on a curve, because I was going to extend the scenery out a bit on either end to hide the fact the track is crossing over itself there. Thank you everyone for all the good ideas.
In the last two weeks I got a little more done on the upper level. I decided to increase the height of the roadbed supports where the track goes over the lower level by 1/2 inch. That gives me plenty of clearance with this car that is taller than all the rest I own.
Since the highest point will be higher, that would make the grade longer (which I don't have room) or steeper. Well that problem was solved when I decided to not try to make the roadbed on the grade out of wood as I have done in the past. I knew I would have trouble making a smooth transition at the bottom of the grade with simple tools and limited skill. I decided to buy Woodland Scenics foam incline sections. Since they come in 2%, 3%, and 4% grades, I decided I could handle 4% as opposed to the 3.7% grade on the plan. If I had a large layout, they could get expensive, but with only two short grades, the cost wasn't a problem. Here are a photographs of the grade already glued down. The paper cutout of the SCARM plan sits right on top of it showing I got the curve pretty good.
I'm going to glue Homasote and cork beveled roadbed on top to give something solid for the track screws to grab. You can see I do have to do a little matching up at tht top of the grade at the last photograph.
Thank you for taking a look!!! Stay safe and healthy everyone!!
Mark, that'll work! 
Looking good, Mark!
Peter
Coming along nicely Mark! Grade looking good too!
You are making good progress Mark. Keep it up and keep us posted.
Mark, looks like you have a good plan! I am with Lew I think it will work just fine! Its nice to see you got it figured out! Keep up the nice work!
Looks good Mark. Sometimes its best to accept our limitations and call in (or buy from), the pros.
Bob
Lew, Peter, Lance, Jim, Mike, Bob, Thank you very much everyone!!
Yes, It has taken a while to figure it out, and there is more to figure out. I suppose everyone runs into that on a layout build. Fortunately this was fairly inexpensive to buy from the pros. If I had more disposable income, there are some other things I would buy too, but on the other hand, I don't necessarily need them. 
I like what you’ve done Mark, not only with the styrofoam for the grade, but you’re maximizing what you have on hand. Well done 👍🏻
Andy
Andy, Thank you!! It would be nice to buy all new top of the line wood products, but then I wouldn't have the cash to buy the rest of the track I need! It will all be covered with scenery, so as long as it is structurally sound, it doesn't matter if it is a mix match. I am rather OCD, but after 35 years married and raising 2 daughters, all far messier than me, I can live with the mix match! 
Hi Mark,
You may have already considered this, but on my last layout, I too used Woodland risers for a double mainline. After installing the risers I applied a few layers of plaster-cloth to increase its rigidity and it also gave much better support for laying and keeping the trackwork in place. It was cheap, easy and fun to apply. Just a thought.
Your progress is great! Keep having fun.
JohnJr
JohnJr,
Thank you for the suggestion. Yes, I can see how the plaster cloth would give something rigid to support the track. Your comment addresses the issue that I am facing since I made the decision to use foam to make my grades instead of wood.
My original plan was to put down a base of wood then put simple 2x4 risers on top of that for the grades and level upper track. I would then use a wood-Homasote-cork sandwich for the roadbed whether on level or a grade. I happily went on with that on the level area then felt overwhelmed at making the transitions from level to the grade. That is when I decided to use foam. That was fine until I realized I didn't have a good transition from the existing risers to the foam.
This photograph shows two mismatches. On the left, you see the top of the 4% grade which comes up to the top of the risers. When I shimmed up the Woodland Scenics grade with 1" blue foam, I forgot that the risers were cut to have 5/8" of plywood or MDF/OSB before putting down Homasote on top. That's the first mismatch.
On the right, you see the risers shimmed from 5" to 5 3/8" to give more room for trains to pass under my one overpass. Carrying that through, I would still need to shim the middle section of risers to 5 3/8". That means I need to raise the grade even further.
Here is where I temporarily placed sections of plywood down to make sure all my shimmed risers are level and at the same height. I will need to work from that overall height around to the grade I showed above.
So in effect, I have been spending some time spinning my wheels on this, but all is not lost. One thing is certain. Everything is nice and solid so far!
I have been thinking of adding more blue foam under or on top of the Woodland Scenics foam to make up the difference in height. Other suggestions are welcome.
Have a great week and stay safe and healthy!!
Great progress, Mark! I'm enjoying watching your layout materialize.
Firewood, Thank you!
Mark- once you have the top height locked in, you can shim the track coming on to the grade. Get a pack of shims from HD/ Lowes. They are cheap and easy to work with.
Bob
Bob, Great point!! I had some, but used them all up when I realized my metal brackets were slightly more than 90 degrees. I was at both stores last week looking for an obscure plumbing part, but never thought of looking for shims. 
I'll have to stop later in the week when I have to go out that way again.
I think those are the plastic wrapped packages of Cedar shims. You get a bunch, cheap. Wish you were close, I have a whole bunch of those left from various projects.
Jeff
Hey Mark, been a bit since I got my eyes and nose over the other topics to take a good look here. It looks great. I love how the grade foam is working. I sort of wondered about that myself seeing it done on a smaller scale(HO) and how it would work. Remember that the only mistakes you make are the ones you decide not to correct or don't notice. Even at that though if you can live with them, so be it. Now, if the entire train flies off the tracks(God forbid), then it's time to stop letting me help, not that I have yet, just saying.
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