I have a '91 RS that originally had a L03 in it, so the oil pressure sending unit was located down by the oil filter. However, I'm swapping in a rebuilt 355 TPI motor built around a '72 block, which doesn't have a place for the sending unit right there, looks like there's a plug there or something.

I see that the older motors have the sending unit connected to the threaded hole at the back of the block near the distributor, just wondering if they wire up the same, and maybe a part number of the right sending unit to buy

 

you can either remove the plug next to the oil filter and put it there or use the one to the driver side of the distributor. they both connect to the oil valley. If im not mistaken, if it has more than one wire on the connector then it has to be hooked up correctly or the the fuel pump wont work, it gets its power through the oilpressure switch so that if it doesnt have oil pressure the engine wont run

 

yeah the thing is the hole by the oil filter doesn't appear to be threaded, there is a plug there, but no apparent way to remove it, it sits flush with the block and is perfectly flat.

block casting number is 3970014, date code January 1972

 

they make a brass adapter that screws in next to your distributor hole that you can screw two oil sending units into. I know for a fact cause ive used them. Thats if you need two sending units, one for the fuel pump and one for the guage. The big fat one that looks like a d size battery and has a one wire connector is for the gauge, and the long one that has either 3 or 4 wires is wired to the fuel pump.

 

actually I just went ahead and drilled out the plug, I noticed after removing the oil filter adapter plate that I could drill into this without getting metal shavings inside the motor.

Looks like I've got plenty of material in there to tap it for the oil pressure sending unit, that way I can keep everything in it's original location, saves me wiring headaches later

Sanity check, the hole should be 1/4" NPT, correct? Which means I should drill it to 7/16