I am assembling a Pole Position right now and just got the power situation going.
AndrewB can sell you two AR boards. It will plug right into that wiring harness and work just fine.
No special schematic hack job needed...And the raster power brick WITH the isolation transformer can be acquired as well. The harness will go right into that.
Its much easier to do it the easy way and plug in original boards in this case. I have like 5 spare switchers on my bench..brand new....and I use them in games where I only need to deal with power...and in games where the iso transformer is separated out. In Atari, things are bundled all together...so using the originals is best. I have rebuilt my Asteroids AR boards (dont work in Pole Position) several times now and its not hard at all. I have spares even.
If you do this, you have original equipment. The Pi Position plugs right into this same harness. It is what it is designed to do.
I understand you have an audio amp, etc, but if you intend to use old Pole Position hardware, its advisable to get the whole package. If you want a modern day bench setup, then treat it as a desktop computer. The Raspberry Pi and software used here is pretty flexible in that regard...its just Mame.
R