I believe that NA gearboxes are numbered 134 Is a gearbox numbered 164 an NB gearbox and does it have the same ratios as the NA box or is it like a PB box? What is the difference between 134 and 164 boxes?
The original gearbox installation on the NA and PA are identical. The PB and NB gearboxes are identical. The J2,PB,NB use identical gears except of course the input shaft on the PB and NB is longer.
Therefore it is the original PA and NA boxes that are the odd ones, easily distinguished by the first and second gear being bolted together and not like the J2,PB,NB machined out of one piece. The PA and NA first motion shaft gear has a male end where the the third gear slides onto it.
Not all NB cars were fitted with the PB gearboxes. Early NBs (like mine) have the PA gears. I think the factory used up what earlier parts they had left first before moving onto the designated upgrades. Terry.