Skip Fix

All depends on how aggressive the HR cam is-factory uses pretty mild ones and the valve spring pressure is also pretty weak. Even the "Hot LT4" is fairly tame. The GM Fast Burn heads I checked that have the First version dual springs is barely 100 on the seat! Spring pressure is what will pull the press studs out and even an aggressive flat tappet should have a little more spring pressure. .Only real change for an HR since they are billet is using a melonized(bronze or composite also) distributor gear like all the 90s Vortec 350s did.

Two different options pinning the factory rocker studs-like all the Hi Perf 409 heads from 62-65 were from Chevy, kits still available. Or if at the machine shop getting a valve job enlarging the valves and new hardened seats have them machine for screw in studs.

toddalin

Was hardly any more than a quality rebuild that was necessary anyway..., 35+ years ago. Back then the heads were $300 and port matching the manifold was another $30.

Skip Fix

Another thing to remember if the cam swap was 35 years ago cam blanks and lifters had a much better quality back then. Even the big manufacturers have had issues.