installing mechanical oil pessure gauge - have ?

i put my water unit in the lower manifold and the oil in extension on the side of the block just take out sending unit and put in fitting with line. good luck

For OP, you can either use a Tee fitting or remove the hex tube and tap it for the mech compression fitting. Your choice. A tee is easier probably.

Never stick your probe in an unknown dark hole. No on the radiator. Dont even try it.
The best temp location is the stock one, so I would relocate your stock gauge elsewhere (to the rear of the driver side intake manifold is where mine is). You can also get a cast t-stat housing from AZ/DAP for 10 bucks, which will accept your stock sender, or get the chrome FRPP piece for 25-30 bucks. Both work, both have drawbacks.

Then just put the new sender in the stock location. Be aware that if it is a mech temp gauge, you will probably need an adapter from Autometer to get it to fit.

Good luck.