Fordged 318-3 truck crank or Poly crank, need help ID

The Poly crank and the 318-3 crank will interchange without issue in the block. Your only possible problem area is the pilot hole size & depth. The 8 bolt flange is odd to get but not hard to get a flywheel for. Just look in the "Racing" sections when looking for parts. Your more likely to find it there first than in the stock/OE sections.

You got a good deal.