Roller and non-roller block differences
 

whats the difference between a 302 roller and non-roller block. Is it just the lifters and the hold downs for the lifters or are the lifter holes machined different? Can i just put roller lifters in a non roller block and make hold downs for it?

The roller 302 blocks have taller lifter bores to support the taller factory roller lifters. But, nothing is keeping your from running a mechanical roller cam in a non-roller block as mechanical roller lifters are the same height as non-roller hydraulic lifters.