Hey Goody, I'm looking into the same thing. I'm thinking Autometer pro-comp Ultra-Lite guages. The holes are 2-5/8 but this dash here looks to have the guages sunk in further. I'm thining he used the 2 1/16 guages and the 5" spedo and they all sunk into the holes. That way you don't have the guage trim sticking out, but sunk in. Not sure, still trying to get more info, mainly on the mechanical spedo as you mentioned. Check out how the guages sit in this dash, looks pretty good.
Dave