340 main cap fit?

I have two 340 blocks one had one main cap only so i got some from a a-body member . the cap on the engine was 2 1/4 '' from top to bottom ,THE SAME AS THE OTHER BLOCK . the caps that i got were only 1 7/8'' from top to bottom . The trouble is the bolts bottom out before there get tight . So if i have the block line bored with these caps they won't fit for sure . does anyone know why they are different size other than they were cut at some point? thanks Couper