I am not familiar with an m20, is it overdrive? what did it usually come in?

3.23 is not low in my book, how fast are you trying to go, 130mph?

Seriously though, this site may help with figuring gear ratios, and speed.
http://www.drivetraindirect.com/t_gear_calculator.htm

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-