Mancini/HS 1.6 rocker not giving me the lift expected

I wouldn't use a checking pushrod with anything other than a checking spring. That's the first thing I'd look at.

Are you 100% sure you're on the base circle when you start your measurements, and also set preload?

What are you using to measure lift? Can you share a pic of your setup? I had to make a big to adequately attach a dial indicator on my heads. Mounts to the valve cover holes.
Yes, started on the base circle and turned several times. The dial indicator was stable. It reliably returned to zero each time as I rotated the crank. Lash was set to zero.

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