What temperature sensor do I use in new style head?

I have the same issue, I have 2 ideas. Instead of the sensor I'm going to put a tee in the adapter, and on one side of the tee put in the original sending unit and on the other side, the bulb for an aftermarket style temp gauge.
The other idea is to find a sender with same ohm range and 3/8 pipe thread instead of the original 1/8 pipe thread.
In the old days of paper catalogs, they all had a section in back of them called a "buyer's guide". It showed specs of the part along with a rough fitment guide. And best of all PICTURES!!!! Of said part/ or at least, a line drawing or sketch.