Were not those transaxles a hybrid made up from a BorgWarner gearbox and an Early Ford ('28-'48) crownwheel and pinion ?
If so then the crownwheel and pinion can be obtained from early Ford parts suppliers such as Macs.
www.macsautoparts.com
That rings a bell with me too. Many specialist speedway manufacturers make Ford V8 ring and pins. As they are still used in lot of quick change diffs. The road car gears are harder and more brittle but wear for ever wheras the 'race' sets are softer, less brittle but do wear out in a moderate time. If they fit use the race ones, ideally 3.78 if it will suit as the 4.11s are smaller in the pinions and break them more often.
Classic speedway guys are using these and do not break them even with nearly 500hp Chevs.
And leave all the 70y/o ones for the restorers as they are all old and fatigued. Acceptable for a std sidevalve but not racing use.