While I've put rollers on plenty of small steamers, and even some larger ones, I don't think this is super realistic to tie the locomotive to a set of specific trucks, at least for me.
As for the cap causing issue with DCS, the answer is no. Right after that bridge rectifier, there is a giant electrolytic capacitor anyway, the DCS signal is tapped off before that point.
I don't understand the "fully powered trucks" comment. We're talking about a locomotive here and tieing into the electronics. So, we already have drive motors.
