AAAAH thank you. Yes the existing vent is from the old A/C but that has been dispensed with as I'm going to be running a soft topper and humidity is not an issue here. I'd assume that the manual vent is the same on teh C10/20 and K10/20 trucks from 1975 also that do not have A/C. Guess its another trip to pick n pull.
Also if I do that then mine would be available for dispatch thereafter.