[Held for Ransom]

I think it had to do with the size of the drive gear fitting in the tailshaft.

[Baron Von Zeppelin]

Here's a Ram3 4spd 3.90
Ram4 Auto 3.90
Ram4 4spd 3.90

All are 70 Baltimore
Marked pertinents with Lime Green
3.90 code is X K
4.33 code is X M

Hope you have enough left in one of the areas to work with.
Holding up to a lamp with good reading glasses or magnifier can help too.

['ol Pinion head]

Originally Posted by Held for Ransom

I think it had to do with the size of the drive gear fitting in the tailshaft.

Believe HFR is correct. Need to examine drive gears from never been messed with original Muncies in front of 3.90 & 4.33 of '69 or 70 G70-14 equipped GTO's.

Believe we will find the drive gear in 4.33 car is a 6 tooth. Its been over 15 years since went down this road, but that is what I ran across. An original 3.90 equipped car ought to be a little easier to find to confirm tooth count. 7 tooth, 8 tooth?