Unless you are interested in PolyDrive in some historical sense (as Carey may be) it would be far easier to start from scratch, with decent drivers.
Let me recommend that you look for a Lobaugh Pacific to get started in major restoration. You will have quality parts, and still a lot of soldering and fabrication to do. A Scale Craft or Hines could also serve as a springboard, but test the drivers for insulation on those.
This one may not need a boiler barrel, but it sure needs new everything else. Carey usually does ok, so he will survive this debacle.