The main point on these swaps that are swapping in a V8 where a flathead 6 was is the steering column!
This is the main point of interference. The best bet is to look at A Body applications, since they also have a narrower engine bay and an intrusive column. I don't know of any A's that had a poly in them, so I'll bet that is going to be the stumbling point you need to address.
If you are going to do a stub frame, frame swap or change the steering, this can make more room. However, it will still be the tight spot (starter, steering, exhaust).