I had the same senario, no oil pressure, when I rebuilt my 86. The machine shop forgot the oil galley plug. I diagnosed it by pulling the oil sending unit and slipping a ty wrap down the hole. It's pretty easy to tell if the plug is there or not. I just unbolted the motor mounts, hoisted the motor, (a body lift helps here) dropped the pan and installed the plug. Boy was that a restless night though!

'86 22R Bored .080", Stroked 5.5mm, LC header, Downey 2.25" SS exhaust, 33" SST Coopers, 4W disk brakes, T-Case brake, PRP Seats