Olds early heads late block

[Clutch]

Ok olds guys years ago I knew the answer but now not so much. What has to be done to early big block olds heads to run them on a late block. For example if I put B heads on a 455 and I don't mean hardened seats. I remember something about pushrod clearance but I don't remember the fix something like drilling the pushrod holes out in the heads. Please one of you guys remind me.

 

[DRIVEN]

My recollection is the early stuff is 45* and newer is 39*. Your B heads will likely need the pushrod slot elongated to work on the later 455 block. Doable but a bit of a hassle.

 

[Clutch]

My recollection is the early stuff is 45* and newer is 39*. Your B heads will likely need the pushrod slot elongated to work on the later 455 block. Doable but a bit of a hassle.

I thought it was something like that I seem to remember there being a way to drill them larger for clearance I'll have to look into it