Can you mount it to the oil pressure tap on the top rear of the block or should it go down near the oil filter?

top rear is the common place on the sm blocks and if you use an alarm sender or fuel pump shut off mount on side above filter

Believe me to get true oil temp readings they must be taken from a remote cooler setup or a remote filter housing. The problem with block mounting is it will read block temp, it should be mounted remotely in the oil stream. Some after market coolers have a fitting for a sender, you can also poke around the find an old Merc remote filter housing off a Merc Hi Perf setup. My 300 Tempest filter has both a sender boss and pass through ports for dual filters.

Phil

If you give me an Email AD I can shoot you a shot of the Merc housing.

Phil