Post a picture; but it sounds like you have the old muncie 3spd from the 50's. As Kelly said; the M20,21 and 22 are all aluminum cased 4 speeds.
If all you need is the ratios; theres no guarantee that what the General put in that case 50yrs ago, it exactly whats in there after 50yrs of service and owners. Your easiest answer is to put the trans in 1st gear and turn the OUTput shaft 10 times, and count the number of times the INput turns. then divide that number by 10. There may be enough slop in the transmission that you wouldn't be able to find the difference between 2.4 and 2.7 for example by only turning it once. Hence the "10 times" method; it'll cancel out most of the slop. Do this for all your forward gears and you'll have your ratios.
Definitely post a picture