not in the service manual

hey all: so the 76 360 had some sort of catastrophic misadventure, so I'm putting a nicely freshened '71 340 in it's place. I'm close to priming the oil pump and reading old threads I came across some chatter about a plug that is in the motor near the distirbutor. Can't find this plug. (or a hole) will it become apparent when I take out the dist. gear? Also I had to use the oil filter base from the 360. Behind it was 3 holes and one was plugged. 340, all three holes are unobstructed. So I put the plug in the 340 and mounted the base...I assume I need that plug, no?

thanks (lots more questions to come)