my buddy has a 68 delmont with a 425 and was wanting to know if 455 heads will fit and if so any mods that need to be done

 

Yes, they will work. In fact, the same C casting heads were used on the 425 in 1967 and the 455 in 1968-69 (as well as on both the E-block and G-block 400 motors). The only possible issue is pushrod clearance, depending on the lifter bank angle of the 425 block.

 

Joe is correct. But, If it is a '68 Delmont then it's already a 455.

Gene