But to answer OP last question, not for sure what "hole" you are referring to.... I would just go to your friendly auto parts store and buy the sender/installation kits for mechanical gauges, they usually have all the various sized brass reducers/fittings you need,included in the kits. The OEM oil sender will unscrew using the 'dial' looking thing, but not by hand, a wrench or even better a socket made for senders. (yes they make them, the auto store SHOULD have them). It may well be a 1/4" npt, in that case remove the (what looks like) the 3/8" bushing from the oil line and screw the 1/4" fitting (that is on the line itself) in its place. You are going to have to loosen all the fittings anyways to let them turn without twisting up the line, and same on the water temp. I would put it where the OEM sender is located also.