I know there are people out there who upgrade conventional engines to TMCC. Can you do the same to old postwar engines?
Of course, it’s no different from upgrading a modern pullmor-equipped engine.
In fact, the first TMCC board which Lionel came out with, the LCRU, was only for controlling Pullmor motors.
The only caveat is that in the smaller tenders, you would probably need to remove the whistle in order to make room for the TMCC boards.
You can get boards from Train America Studios, Digital Dynamics, and The Electric Railroad company.