Both tachs are Sun but I have not seen a control box, I know what you are talking about regarding the box. I have not traced the wiring for them but they appear to be connected directly to the coil, there are a lot of wires there. I am a little nervous about that as I intend to install an HEI distributor and while it has a tach terminal, I have never used it in other than an OEM situation. I don't know why Bean would have not used the factory tach or the factory gas gauge, it is taped over in the original location and an aftermarket IH style gauge and sender were installed with the aftermarket tach. Of course the gauge is funky, works sometime, and the terminal on the sender is stuck, cannot remove the wire as the stud turns in the sender. I am thinking about replacing the sender with a Chev and enabling the original gauge in the dash. In the mean time, I have a stick for checking the fuel level, seems pretty reliable.
The Chev Steel Tilt Cab was built from 1960 to 1980 when Chevrolet quit selling heavy trucks. I don't know about the GMC version, perhaps they went longer. I have seen a couple different dashes but I am not sure if that was due to the year of manufacture or Chev/GMC leading to the differences. Same thing on the grills, a couple changes with Chev/GMC being different.
I will get some pictures of the truck soon.
