63Step,
I was looking at your album of photos and noticed you have the full gauge cluster in that C70 cab. That's a major score. You'll want to refurbish that and use it in your C10. A factory original tach is hard to come by and the aftermarket replacements are expensive. There are a few minor wiring changes to be made, but you'll like having the full instrumentation over the standard "Idiot Lights".
Edit: The Tach may not work on your 250. Those tachs were designed to work with the V8s. I'm not sure if it can be changed to work on an I6.
Last edited by 62Stick; 01/24/2018 3:57 AM. Reason: Added tach info.