Missing tender Coupler on 3rd Rail/Sunset MT-4

Probably obtain an mth electrocoupler and/or contact third rail to see if they have an electrocoupler as well.

As far as the boiler front, chances ate good the boiler front was held in by friction and now the boiler front has been worn down so there is little friction to hold it in. Possibly a tiny rubber band around the inner lip of the boiler may hold the front in. If that doesnt work, a TINY amount of jb weld applied with a toothpick may add the missing friction around the boiler front.

Usually you can slightly bend the boiler opening so that there is enough friction to hold the boiler front in.  Pushing the boiler front in rounds it back out.   On virtually all brass locomotives, the boiler front is simply held in by friction.

As for the coupler, you'll likely have to find the mounting hardware as well, the lobster claw mount usually comes off to mount the Kadee couplers.

On some the smokebox front hinge actually works.  My SP2 4-10-2 is mounted this way and is held closed with a curled piece of brass that friction fits inside the shell Others rely on a tight fit where the entire front can be removed.  This is provided where clutter in front of the smokebox makes a hinge more of a hindrance to convenient access.  An example of the tight fit is my 3rd Rail Big Boy, where the forward platform would interfere with a hinge front.

Bruce

Although I've seen a few with the curled brass that you describe, the vast majority of the ones I get for upgrades/repairs simply have the entire front friction fit.

I come by the misconception honestly.  Two of the five 3rd Rail locos in my possession have hinged fronts.  The other being a PRR, J1.

Bruce

I suspect one reason may be I see a lot of older 3rd Rail and Weaver/Williams brass, those are typically the ones that are looking for upgrades.  Maybe the new 3rd Rail stuff is different, I don't often get to take those apart.

Friction fit,  very slight pinch fixes it.  Many different brand brass engines employed this method.

The next stumbling block frequently is metal brake hangers/shoes shorting the insulated wheels.  That was a fun one to find on my first brass engine.

Next up was when a previous owner swapped in scale pilot wheels w/o providing cylinder clearance.

Depending on the style, year, or whatever couplers,  I have some MTH lobster claws couple up to Kadee couplers on my Snyder racks.

I would be hard pressed to put one of those big nasty couplers on the front of a SS steam engine.  Stands out like a sore thumb on a nice pilot.  Opinion. 

I appreciate the input.  The pilot coupler will remain as is.  I'm just interested in the tender coupler.  With that in mind, I've decided to send it off to have full upgrades done and get things operating right.  Only 25 of these made in Daylight scheme....very happy to own this...just time to get it all updated.  Thank you all for helping me decide.  B