I believe there is a flow control orfice in the fitting back at the rear cam bearing passage, the one where the oil line to the cylinder head attaches. Try removing that fitting, and see if there's a 1/16" diameter hole in it. On the early rocker arm assemblies with the grooves inside the rocker arms inline with the weep hole at the top, controlling the oil flow to the rocker shafts is necessary. Later rockers with the offset oil grooves can run higher volume and pressure to the shafts.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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