I'm guessing this is an HV pump and they had standard bolts. If you bought ARP bolts for this app like the ones 440 source sells they are too long... Could be your issue. Otherwise make sure the O ring is good and use a good gasket. Superperformance sells the BEST oil pump gasket available IMO.

Now I need to pin those needles, got to feel that heat
Hear my motor screamin while I'm tearin up the street