goo, sorry about the late reply...I get the impression sometimes folks don't look at mine because there's very little progress.
The tach/speedo are 3 3/8", and the rest are 2 1/16"
I chose them more out of convenience than desire I think...I happened to have a 3 3/8" speedo from my Mustang that I would no longer need due to using an electronic speed sensor, and the 2 1/16" fuel gage is also left over from the Mustang...when I swapped to EFI in that car, I installed a newer tank and the sending unit required a different gage, so the old one sat in the package for a few years until I figured out the old Mopar impedance was the exact same as the old carbed tank in my Mustang...saved me some cash when populating the dash.