In fact, unless "you're expert" it's a little tough to tell a poly block from an LA block just looking. Some guys have made this mistake swapping a rebuilt short block
There's no problem using a Plymouth Poly block when building up an A motor. Those engines tend to have very thick cylinder walls, and I know of one that was poked all the way out to 4.040 (That's .150 over!) and lived on the street for a long time.
Dodge and Chrysler Poly blocks will interchange with their Hemi counterparts, but only the Plymouth will take LA parts.