My first engine swap ever was dropping a 383 six pack into a 73 RR that was a 318 car. Took all summer because (as a kid) I thought it would just bolt in.

After some research, I bought (IIRC) 400 Motor Mounts for 73 RR and I had to change the oil pan because the 383 sump hit the K-member and would keep the back of the engine from dropping down correctly. I went to a JY that had HUGE STACKS of OIl Pans. I spent several hours going through the oil pans until I found the one that would had the sump further back than mine. Don't know what it came from it was in the stack. Once I put the oil pan on, everything lined up fine. I do not know what the 383 engine and trans originally came out of but I pulled them from a 66 Fury a guy had "rodded". I don't recall having any issues getting the transmission to work, however the tail shaft was longer on the big block trans and I had to get a shorter driveshaft which I found in a wrecked big block RR in a local JY at the time.

Car ran and drove great w/ no issues.