I have fitted a sender on a threaded ring I welded to the cylinder head rectangular plate at the rear. Disadvantages are that there is some more work involved and temperature there is actually higher than up front (near the water pump) so it can frighten you... The advantage is that you keep the "too late" red warning light.
You can also put the sender in place of the warning lamp sender. The thread is M18x150, you will not find sensors for all gauge makes though. In the past I had a very hard time finding one for a Veglia gauge, and recently I was told no such sender is made for a VDO gauge.