There are 5 variables that are all related here: rear tire height (=26.6), what gear you are in (4th=1:1),the rear axle ratio, the engine RPM, and car speed.
If you know 4 out of 5, you can solve for the one you're missing.
Right now you are not sure you have a 3.23 axle rear, and you are not saying what the RPM is when you are going at whatever speed.
Since a Muncie 4 speed has a 1:1 4th gear, that is known, and your tire diameter is known....those two are for sure.
If you get on the highway in 4th gear, and can write down that you are going some true MPH, at some RPM...then you can calculate the rear end gear, and go from there to figure out what color speedometer cable gears you need.
Right now all you know is your speedometer cable is turning too slow. As said above, if you check to see what speedometer gears you have know, you may be able to get a few gear colors that are the next few up and try them until you get real close, or do the RPM vs. speed test and calculate it straight out.
Edited by JoePeek, 28 November 2020 - 02:02 AM.