I'd try the simplest thing first, re-tourqe heads and intake. If this doesn't fix it change the gaskets, pressure test, ect.
Hope it's not a crack...
I'd also adjust the bypass spring for the pump to a lower pressure, say around 60psi. This won't effect volume (your oiling system determines how much
oil it will take). It's important to keep in mind the pressures these engines were designed to run. I'd be suprised if your filter doesn't weep a little at those pressures. Most of these engines ran around 40psi (cold) in factory state.