NOT MINE - Hemi parts 392 others

How do I tell the difference between a 331 and a 354? I need a number 3 main cap. It was cracked long ago when it was being assembled. So if I get a new main cap, and a line hone, maybe I’ll be okay for reassembly.
http://www.hothemiheads.com/ these guys could help for sure. http://www.hothemiheads.com/