[Richard (EV8G)]

Originally Posted by JM 35 Sedan

Richard, 3.78's came in 10 spline as well as 6, and 3.54's also came in 6/10 spline. I've only found 4.11's in 10 spline but as sure as I'm sitting here typing this, someone probably has an original set of 4.11's with 6 spline . JM

You are correct that there are/were 3.78's with 10-spline (part number 68-4209-B) and the hollow driveshaft. There are/were also 3.78's with 6-spline (part number 68-4209-A and the solid driveshaft. There is also listed #48-4209-D with 4.11 ratio and 6-spline, but (even though it has a 48 number prefix) which is specified for 38-48 and so would not have been available for 1937,
except that nothing is 100% certain, as you say. #48-4209-E with
3.54 ratio is also listed with 6-spline, again for 38-48, same story.

IF a 1937 (confirmed to be original equipment-but who knows?) rear has a lube fitting on the torque tube, it would/should/probably be a 6-spline with the solid driveshaft and center bearing, and most likely a 3.78 ratio. As the man said, probably need to take it apart to be
sure...