[jailhousebob]

So it sounds like someone made a custom driveshaft or modified the orig driveshaft to accomodate the later rear.Ford pinions were 10 spline through 1936 and went to 6 in 1937.You have what sounds like a 6 x 10 pinion adaptor welded into the end of the driveshaft.Ford actually made this part specifically to allow the replacement of the earlier rears with later ones.They were also available aftermarket for years but with Joblot automotive going out of business last year the supply has dried up.You need to determine if the pinion splines are still good.Assuming the splines in the driveshaft are bad you could have a new one made using tubular steel and a regular ford 6 spline coupler welded into the end and the front of uour existing shaft ( the universal end ) welded into the other end.Sounds easy but the problems are finding a shop that is willing to do it .The OD of the coupler has to be reduced or enlarged ( a bushing welded on ) to properly fit the id of the new steel tube . It all has to be precision fit and welded to avoid excessive runout. You may be able to do the same thing usung your existing shaft depending on how it was modified the first time.In other words,can the offending 6x10 be removed leaving enough length on the shaft to fit the new 6 spline coupler.
Of course ,if the pinion splines are trashed that would require replacement but i have had factory pinion couplers that have had all the splines wore out of them and the pinion splines still be good. Hope this helps,Bob