Need 1965 C10 temperator sensor electrical help - need a parts guru

[markbritt]

Hello:

After a year and a half, my 1966 C10 stepside long bed is 99% done. Here is my problem. I have a 1971 Chevy 350 engine with 1980's heads on it. The 1965 water temperature sending unit will not fit in the heads as the hole in the 1980's 350 heads is too small. I picked up a 1980's "something or other" sending unit that does fit, but when the engine warms up, the gauge goes way over on the hot side (I have an autometer mechanical temp gauge and the engine is running fine). I have spent hours on the web trying to find a newer GM water temperature sending unit that will fit in my 350 heads (smaller hole) AND still allow the factory C10 gauge to work properly.

I believe there are two options:

1. Identify a water temp sending unit with the smaller threads that has the same electrical properties as the larger 1965 unit. (Anyone have an idea??_

2. Locate an adjustable resister that can be located in-line that would allow me do adjust the voltage on the current sender that is showing too hot.

Has anyone found a sending unit that will fit in my heads that will allow the gauge to function properly? If not, what about the adjustable resistor idea?

Any and all help will be greatly appreciated!!!

Here are pictures of the sending unit (1965 on the left, needed size on the right) and a picutre of the completed truck as well as the engine.

Thanks