273 questions...a few of them

Steve do you have a compressor that allows you to remove the no1 springs with the head on the car?

If so, I'd suggest you read what I posted earlier, put light springs on the no1 cylinder, leave all other pushrods out, and try to walk the thing through a cycle (2 crank turns)

Light springs will allow you to push down with your finger as you go, and check for piston clearance. If you don't have a dial indicator or even a caliper with a depth stem, you can "try fit" feeler gauges stacked up as the piston comes "up and over" to check for valve/ piston hit

Look especially for the rockers hitting the valve retainers, IE in the "inside heal" of the rocker.

Again, I do NOT think that a few degrees advance/ retard can cause this problem.

So, what DO we know?

We know the lifters are same "pushrod height" as the old ones?

Same pushrods, or same height?

Same rockers, or same stock type?

Have you checked valve installed height against factory specs? Is either valve stem height "as per factory?"

Don't check for spring bind "by looking" you need to get a feeler or a nail or something in there. Don't forget that EITHER inner or outers can be binding.

I don't know if you posted, but crank degrees where it stops would be helpful.

ALSO if you think this can be a valve to piston problem, it would help to try with ONLY first one pushrod in, then the other. And ONLY install the pushrods for no1, leave all others out.