Is it a fresh motor?
He means crank it with the starter motor, Taking the CAS off means it wont start up.
Like he said, Take the feed line off the turbo and crank the motor over and it should spit out oil if it has oil pressure.
Make sure your guage is properly hooked up.
If it's a fresh motor maybe the oil pump wasn't prepared with petrolium jelly shit. it needs this to create suction to be able to initially pull oil into it to start pumping something.
If all else fails, take your pressure sender out and screw a small fitting into it and using a compressor with an oil can connected, slowly push oil down the pressure sender hole so it feeds back to the oil pump and gives it something to suck with.
Either that or like mentioned before, the pick up could be sucking air, either from your modifications or by not replacing a worn o-ring.
OR the pressure relief plunger/spring in the bottom of the oil pump is stuck open and is bypassing all oil pressure back into the sump.
Start from the beginning and begin the process of elimination.