The a500 swap is near!!! Could use advice

the A500 is from an 318 88 van I have supporting paper work saying it was rebuilt in 2000, it now sits with 56000 miles.

I have a 79 doba with a rebuilt 360 short block, Im assuming it was rebuilt stock.

I have added a summit cam 6901, performer intake and thermoquad

I plan to add 302 swirl port heads with 1.88 intakes in the near future.

The a500 also comes with a torque converter that I would like to use.

I read that I need a B&M flex plate. Could somebody point me to the correct one.

OH !!! And I need to change my rear gears, the doba is a K code so It came with a 2bbl 360. I'm pretty sure based on take off I have 2.4 gears.

Is there a dakota or donor car I could pull 3.23-3.55 gears from that will fit correctly?