Vacuum on 1968 GTS 340 4 spd.

Roger.... I will have to look up that small head. But that still is not enough of a cc difference for 1.5 points in CR. Roller springs are just the springs/retainers. It would have to stack up with head gaskets and deck height differences. This is very unusual.... like you don't already know.

Maybe OK with the .045" extra (with shims). If the pushrods were still just touching the lifters after they pumped up, then yes. If they were loose then that clearance is deducted from the .045" to get the preload. And the 2 sides can be different.