Why not just re-ring it and install a crank kit and a few new rods? Sounds like you had low
oil pressure due to damage at some time that opened up the rod clearence. As long as the mains did not spin you could fix what you have and save yourself a fair bit of change.
Install a new
oil pump and be sure to check your clearences. Rule of thumb is 10 psi per 1,000 rpm. So if you can spin it to 6,000 you need 60 psi when you get it off of idle speed.
20psi is not enough to run a high end V-8.