remote oil filter fittings tapped right into the block UPDATE in post 58 and the whole idea got 86ed

The correct drill size for a 3/8NPT is 37/64 (.578)

Use a 3/4-16 adapter fitting with an o-ring for the big hole. Here is one to go to a -8AN hose (which is probably what you'll be hooking up your remote filter/cooler with): Earls AT985008ERL Earls -8 AN Male to 3/4"-16 O-ring Port - Holley Performance Products