Thanks a lot for the advice.
I found a guy selling a complete 351W (including carb) for 550$ Canadian (400 US). He said it runs fine, from a late 80s Crown Vic. Or he said he'd sell just the bottom end for $350 ($200ish USD). I think I may go that route, or maybe hold out and look for an even cheaper bottom end to start with.
Guess I've got the bottom end plans figured out - now I just need to decide whether I want to go carb or FI.
Thanks again for the help.