I just had an interesting problem with my 331 Hemi I am rebuilding. I sent the block to a machine shop to be cleaned and honed. Everything is in such good condition that I am putting the pistons back in that came out of the engine. The pistons are stamped STD on the top so I ordered a set of standard bore 331 rings for it. The set that came in were way to small for the engine. When I went to check the ring gap by putting them in the bore they just fell through. I sent them back and received another set with the same problem. Very confused now I took a piston down to the machine shop and had it measured. Turns out that it is a standard piston for a 354 engine. My block is stamped 3NE55 so I guess someone in the past bored it out to 3.94 inches and made a 354 out of it. The guy at the machine shop said he knew of people boring a 331 out to 4.00 inches. Anyway, I am glad I didn't order pistons for a 331 because I would have been very upset at spending so much for something that didn't fit. Has anyone ever had a problem like this? In the future do I need to just order 354 parts and forget that the engine was once a 331? Thanks, Hardy