Tom,
I have read that the first model year with a 90 mph speedometer is 1952. Best to get answers from owners of 1952 trucks (and hope they have not been modified in the last 54 years).
Tim
[ Added later: as you most likely already know, Jim Carter & Classic Parts (Chevy Duty) show 1952; but, Chev's of the 40's shows 1951). ]
