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.
I wonder if @RustyRatRod knows. I know he has one done on a stand.