I’m going with this:
Titanium retainers and Smith Bros 5/16" x.116" wall pushrods.
Had a customer with a low deck 511 with a .640 roller and 943 springs at 1.900.
Ended up dropping an exhaust valve.
Sent me the heads to repair.
There were witness marks 1/4” away from where the exhaust pushrods passed through the heads!!!
All the areas near where the pushrods passed through the heads showed that there was a ton of pushrod flexing going on. Enough so that there was not only a witness “mark”, but it had actually pounded a raised lip at the deck of the head.
Again..... that was 1/4” away from the pushrod.
The intake pushrod tunnels were closer to the pushrods, which limited the amount they could deflect, but the area around the exhaust pushrods was much more spacious, allowing for much more flex. The severe flexing is just another way to lose valvetrain control...... and the result was a dropped valve.
They were heavy wall heat treated 5/16” in that motor.