Roller Block: Pushrods Rubbing Against Head

I had that issue with an 88 d100 (318)
My first encounter with '302 heads, I swapped them out with a set of older (probably late 70s) 318 heads since I found out that the original 302s were cracked. This was about 30 years ago.
Just by a head swap I went from an engine with fantastic oil pressure to "none". When I put the heads on I just dropped the pushrods in, put the rockers on, and then the valve covers. When I discovered I had lost oil pressure I went back in to figure out why. At the time my guess was that the rubbing pushrods lost contact with the lifters and that was where I was losing my oil pressure.
I ended up rebuilding the whole thing, and I went to the junkyard and got another set of '302 heads, and had them gone thru. I paid $400 back in '94/95 at a junkyard for the replacement set of 302s, plus I paid for the trip they took thru the machine shop.