The problem with metal couplers and hot frames is magified on my railroad. All my cabooses are brass, and about 10% of my freight cars.
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The chances for short circuits are large. The Kadee 20 series couplers were an absolute blessing.
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-Kevin
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Another option is to cut the coupler mounting extensions off the frame, then build styrene pads under the end walkways, and body-mount the couplers using screws. This also allows you to close the gap in the pilots below the couplers.
Wayne
I converted 2 Athern Trainmasters a long time ago. I don’t remember having any troubles.
I just isolated the motor from the chassis.
I used Kadee Universal Black Box insulated gearboxes to install couplers.
If you decide to remotor for DCC, the easiest upgrade you can do is an Athearn gold motor. It’s a drop-in replacement for the old black Jet 400, and it uses about half as much power at any speed. Here’s one on eBay now with the pads and everything: https://www.ebay.com/itm/3-HO-ATHEARN-FP45-DIESEL-LOCOMOTIVE-DUAL-BRASS-FLYWHEEL-MOTOR-ASSY/302765148174?hash=item467e35880e
To insulate it, stick a piece of electrical tape or masking tape underneath. For electrical pickup from the left rail, tap a screw into the chassis and run a wire from it to the decoder. A 2-56 drill and tap set is pretty cheap if you don’t already have one.
I really think this would be a good project to try and convert to DCC. If you give up or screw it up you can always just make it a dummy. It’s a nice looking loco and since it runs well it seems a shame to not at least try to give it a place on your roster.