RZ, The senders for the water and
oil should be a tapered pipe thread. They won't bottom out because of the taper. Use some teflon tape on them and screw them in until they are tight. If you try and overtighten on an aluminum manifold you can crack it. The
oil sender goes just above the fuel pump on a 351w. It takes 1/4 pipe thread, I usually buy a 3" pipe to bring the sender out beyond the pump. I'm sure you will need to adapt to the
oil sender.
PS, I'm not opposed to mechanical guages at all. You must be thinking of someone else. Mechanical gauges give more accurate readings than electrical.
Don