John,
let me ask you then since your more familiar with GM, are you sure you have factory ford rockers? take some pics of the rocker set up.
checking clearances may take more than you think, applying
oil pressure with the valve covers off would let you see any excess losses there.
you could spin the motor with the ignition disabled or pull the distrib. and spin the
oil pump with a drill to see if you have excess leakage out the sides of the rockers or shafts.
the restriction size you stated seems right in line with what others are running.
are you absolutely sure your
oil pressure gauge is right? just so your not chasing ghosts. tick or no tick, is it oil pressure or just bad or worn components.
just for the sake of making sure add an extra quart of oil and see if the oil pressure goes up.