This new 3:88 ring and pinion has got to be on your list for an upgrade to your old tried transmission. This is what the transmission builders use to make freeway fliers. This gear set has a Keyed style pinion and come with the pinion nut. This is bought as a matched set. Will not fit 1968 or newer Bus.
Needed items to go with this ring and pinion would be:
transmission gasket set (113398005A or 1133998005AGR),
Syncro rings (1st 113311269A, 2nd 113311269B and 3rd-4th 113311295D,ea)
CV flange seals (113301189F)