Frank,
I have ten of the Walthers Mainlines and added metal power pick-up trucks and SMD light bars with the kits from Walthers. The cars are the same as the proto ones without all the detail. If You want body mounted couplers, they had a kit that You could purchase the swing arm couplers for those cars. No need to do any drilling or cutting to install. You could keep the trucks that came with it and cut off the draft gear.
The swing arm draft gear looks like the photo…just have to screw on:
The couplers are Protomax that came with Your models…no need to change, just about the best Kadee clone around.
Take Care! [:D]
Frank