Just from looking at the pictures on ebay of the bellhousings, it looks like any aircooled Porsche tranny would bolt up. Getting the clutch sorted is another story... Plus they are a LOT bigger/heavier so some serious fab work for mounts and massaging of sheet metal and then there's the ever popular problem of gear ratios not compatible with VW power curve.
But still... I ain't skeered
, the GL bus will have a tranny transplant of some sort.