Ok heres what I got, just purchased a 91 gt with stock bottom end, prob a e cam, gt-40 upper and lower with 1" spacer, stock fan, and I just put on a mech oil pressure gauge by autometer(now i did not put directly into block I put it on the bar where the elc gauge attached to) if that helps. Crank it up and I get about 60 lbs of pressure and about 20 lbs after warmup while driving BUT at Idle it drops to about 10 lbs IS THAT OK, nothing sounds funny in the motor like lifters rattle or...

Oil pressure problem with 1991 Mustang GT