Please advise on valvetrain issue.

I had GT40 (not milled) Cobra heads with the factory 1.72 Crane pedestal rockers. I removed those heads and traded them (with cash) for a set of Edelbrock performer aluminum heads that look new but are used. I got sidetracked with life and other priorities and the mustang went on a back burner...a year later I decided this weekend to put it back together.

The Edelbrock heads came with the same 1.72 Crane rockers but had .030 shims. Even though the heads were not milled I put it back together with the shims left on. After I fire up the engine, it is running with a bad miss and the rockers are knocking like rocks in a can. So I take the valve covers back off and removed all the shims, as I was doing that I noticed on the # 2 cylinder on the intake valve the rocker was loose, even after removing the shim with the valve closed, it has almost 1/4 of an inch free travel even after being torqued to 20lbs.

I suspect a flat lobe but it ran fine and was quiet before I tore it down (90 roller motor) and I do not see how a collapsed lifter would do this. The push rod is straight as an arrow. I ran it for a few minutes and shut it down and now it sits again. What should I look for to diagnose this? Thanks in advance!!!