I want to build one of the 455's I got. Out of the sets of heads I have, 2 "C"'s (small valve) and "B" (needs seats), "A"'s are the only ones I could bolt on without much rework. I did a port and polish job years ago on them. Now after some research and reading the "Engine Modification and Tuning Guide", I realize the different lifter bank angles and that the pushrod holes need to be opened up to .562 (9/16"). The holes now are roughly .5 (1/2"). I don't think I could open up the holes that much without busting through the intake port wall.
Does anyone have any experience using "A" heads on later blocks. Can you get away with maybe boring out the bottom half of the hole? Maybe it's a trial and error thing. I really don't think I could bore out the whole hole. Maybe a thinner push rod. Thanks.

Dan

 

Using a drill is the easy way to open the holes, but you really need to slot them in the direction of pushrod motion. You can probably do that with a die grinder and not disturb the port walls. You may just want to try a mockup of the engine without doing anything and see if the pushrods even hit. You do not want smaller diameter pushrods, as this significantly lowers the buckling load that the pushrod can carry.

 

Thanks for the reply.
I'll try a dry fit first. To be honest, I edited my original post by removing some content, but I had run these heads on an "E" block many years ago cause I didn't know the difference. Didn't run it long so can't predict what the actual outcome would be but I didn't notice anything after the short time running it, no damage or signs of rubbing. Since this is a different block and about 25 years since then, I'll check it out first, maybe I'll get lucky.

 

If you do happen to poke through the intake runner,you can have the pushrod holes sleeved,then blend around them in the runner.That is what you have to do anyway for the strip/allout port jobs.