Can't Fix Stupid, but How About His Train?

Pretty sure you can put that dog back together!  Doesn't make you feel better of course.... but it is certainly fixable! Re-stake the original studs... no reason to by replacement trucks, that would be crazy!

Thanks, @Dennis Holler.  Do you have a guess as to where the washer/cup goes and its orientation?  I've played around with it and nothing seems quite right.

The washer cup goes on the truck stud. The cup[hollow portion] faces down onto the truck plate the truck stud with the e clip grove should show above the cup and when placed onto the frame the e clip holds the truck to the frame.

I have the Milwaukee version of this cab-less dummy.  The stud is pressed into the truck.  A little JB weld may be a good fix for putting it back in the truck.  The cup washer goes on the stud with the big open end on the truck.    There is a ring on the truck in your picture that  seems to match the cup washer diameter.  The stud then sticks through the frame and is held with a retaining washer or c clip.

On mine, the c clip is also the ground for the lights.   

Here is a picture of the c clip on top and a picture of the cup washer between the truck and the frame when assembled.

Thanks @prrhorseshoecurve and @VHubbard.  That helps a lot.  I'll be tackling this later today and tomorrow, and post my results.  Just because I know 'what' to do does not mean I can do it!

Although the comments of @Dennis Holler and @prrhorseshoecurve are helpful, thanks especially to @VHubbard because as they say “A picture’s worth a thousand words.”

Don't feel bad. My around the wall layout in my loft has a stair access with a wood hatch to cover it.  I usually close it when running trains, but it was a hot day and wanted the air movement so I left the hatch door open.    I had a similar loco, a Lionel GP9 Southern RR,  decided it not only needed to derail, but take an Olympic pommel horse jump off the track down to the bottom of the wooden stairs, and came apart as if someone was filming a train wreck movie and blew it up.  Amazingly, as in your experience, the body was fine, but had to replace one truck, not because it was mangled on impact, but because one of the plastic studs holding one gear in place,  sheared off.  Between 'The Traintender', and Trainz, you can always find the part you need.

Partial success.  As the picture shows, I was able to hammer in the special rivet and it appeared to hold onto the entire truck well enough.  I then put the washer/cup onto the truck assembly with some super glue, and then put the frame over the trucks.  I secured the e-clamp on the rivet, and it was off to the races, or so I thought.  Since I had the unit apart, I looked at the lighting (front and rear head lamps and number boards lighted with a bulb apiece).  I discovered I put some LEDs in there a year or more ago.  The directionality of the LEDs weren't bright enough to light up the portholes, so I added another LED, and the lighting effect was great.  I started my victory lap screwing the body onto the frame, but unfortunately at that point the rivet didn't hold one of the trucks that well, so it fell off.  I just walked away at that point, and will try again tomorrow.  Never say die!

...hammer in the special rivet..

Rivets are normally put in the hole and then expanded on one side to hold it in place.  Just putting the post  back in won't do it.  If you have a punch or drift, you can put the top of the post resting on something solid like the jaws of a vice, and hit the back side to expand the rivet wider into the frame.  Best to have someone hold it while you hit it. If you have drills and a tap and die set, you can drill and tap a hole in the bottom of the post, and put in a machine screw of appropriate size,  2-56 maybe, with a flat washer to hold the post in place.  Last but not least, if you clean the metal to pure metal, remove the bluing, clean the bottom of the post  put the post in, you can solder it to the frame with an ample enough solder gun, 140 watts or greater,  or old style solder iron, the ones with a pyramid tip in the 1/2 inch size.  Make sure nothing plastic will be heated up.  The larger the source of heat, the faster the joint will heat up and take solder, whereas a smaller iron or gun, will take a long time with an expanding heat wave that goes everywhere before the solder will melt at the joint.

Thanks @CALNNC, unfortunately the space under the frame in my pic isn't easily accessible.  There's some type of metal plate just hanging there that completely blocks access.  It has absolutely no purpose that I can discern.  My guess is that it might do something if that truck assembly had another purpose than being on a dummy engine.  I'll take a pic tomorrow.  I do have a big solder gun and will probably work to solder it in place.

Worst comes to worst, a couple of nuts and bolts will do the job. Make sure the bolt faces down... 

Mitch

In the first picture I'm holding the truck assembly upside down.  It hopefully shows the limited space under the top of the frame of the truck assembly.  It is blocked by a metal frame which was added to the assembly, and it looks to serve no purpose.  The second picture shows the stud soldered to the wheel assembly.  It seems very sturdy, thanks @CALNNC.  I thought I was done, and as I'm actually putting the engine in the box, the truck assembly I put on without soldering came off!  Once again, I walked away and will resume my journey tomorrow.

Finished!  I used the soldering suggestion from @CALNNC to attach the second post (already did the first) securely to the truck assembly.  I stress tested both by holding the post and shaking it, no problems.  Before I zipped it up, I upgraded the LEDs to add one to have some light coming from the portholes.  The top picture shows that.  When I saw that I realized you could look through one porthole and see out through the other.  I happened to have a plastic generator from a discarded searchlight car, so I put it into the dummy shell.  It actually was a perfect fit.  The bottom picture shows the generator through the porthole.  I know it's not prototypical, but it looked better than an empty space.