How would you run that filter linked? Do you need an onboard compressor?
After researching these filters, the air is only for drainback - there has to be an air gap at the bottom of the unit for the oil jets inside to spin the rotor. The air pump lets you drain "under pressure" uphill, like on Project 300. As long as you have a nice, large opening at the bottom for oil to drain from(1" or better), you won't need air.
Using the oil pressure to drive it, however, presents another problem - you need decent psi. 11 psi at hot idle won't cut it; i think that filter requires a minimum 27 psi to operate.
Hopefully you are running an electric fuel pump. I would just drill and tap your original mechanical pump block off plate with a fitting to do your return there.
I personally don't trust electric pumps after a nice duralift failed and blocked off the fuel. Not just let the ip pull it, blocked it off and left me stranded. The mechanical pumps will "flow through" as will some (generally cheaper) electric pumps.
I've had at least one catastrophic mechanical pump failure(Leaking a lot), but it didn't stop me in the iddle of the road.
After looking at my heads today while porting them, Macrobb's right those plugs do go right into the oil drain back holes in the heads. I'm sure it would not be fun to try to get those plugs out though.
Harbor freight allen to 3/8 square drive adaptor is what I'd use. (On mine, those plugs are allen headed)