Trains

Hi, I'm working on a fiction project set in a rebuilding society 100 years out. It's fairly utopian so people are prioritizing restoring and improving train infrastructure and service pretty significantly. American cities have high speed rail connecting them, and because I'm building this story out of my daydreams, defunct short lines have been returned to service and even rural towns have some kind of passenger train running again.

The opening has the players traveling way out into the boonies, and part of setting up that 'traveling off the edge of the world' feel was having them leave whatever city they begin in by HSR, then take successively cruder public transit until the line just ends short of their destination and they have to figure the rest out on their own.

The second-to-last step in that chain is an electric self-propelled railcar traveling along a restored short line. I think the current doodlebug is a somewhat-recent thing, put together maybe within the last ten years, and probably planned to be temporary when they built it.

So my question now is: how would they build this thing? Would it be easier to convert an existing self-propelled railcar like the Budd RDC? Would it make more sense to start with a regular coach and retrofit in the batteries, motors, control station, pantographs etc? Or would it make more sense to start from scratch? Maybe use part of an electric bus or similar?

Reuse and salvage play a pretty big role in the story, so I'll probably embellish any option with details about where the parts came from originally.

Thank you for any advice!