Get a speedo app for your phone. Drive 50 MPH by gps, the dash speedometer reading either + or - X2 will give you the ratio you need , then find a ratio adapter to speed up or slow down the speedo cable by that much.
BC 1960 Chevy C10 driver 261 T5 4.10 dana 44 power loc 1949 GMC 250 project in waiting 1960 C60 pasture art Retired GM dealer tech. 1980 - 2022
