Roller LA cam in a Magnum?

I've also read where the older heads (don't know what you are running) don't have enough clearance for the pushrods with a roller cam, because the taller roller lifters change the PR angle through the heads, I believe.

I'm "about to find out" about this if and when I get my J heads back which are going on a roller block. I will however be using the smaller dia. adjustable pushrods, which I hope to be able to shorten myself.