markeb01 has a great thread on Sun Tach's
http://67-72chevytrucks.com/vboard/s...d.php?t=392461
The vaccum gauge will work on the six no problem.
1966 had an optional 3 speed automatic. This gear selector prism may not line up with the newer 3 speed positioning however. Perhaps if you look in the 67-72 restoration places you might find a 3 speed clear prism for your shifter but I'm not sure it was the same style, anyone have an idea?
