[Tony_D]

I have a 200-4R transmission out of a 1985 Monte Carlo SS that I want to put into my 1966 GTO convertible. The car is a 389-4bbl with Super Turbine 300 trans.
It has 3:23 rear end gear ratio where the Monte Carlo came with 3:73 so I believe I need to replace the speedometer gears in the transmission so the speedometer indicates correctly.

I found a chart that determines what speedo gear ratio you need (drive gear/driven gear) based on tire size and rear end ratio. Using 26 inch tire and 3:23 it says I need a 0.399 ratio. The closest on the chart is 0.400 which corresponds to 12 tooth drive gear and 30 tooth driven gear, GM PN 8634935 and 561035 resp.

Can someone verify these part numbers and my thought process?

Thanks