Unfortunatly guys, the OD ratio is materially the same. To see the ratios of the various trannies go to Gear Vendors site, they have ratio charts for all popular trans.
At the risk of a hijack here, I have found the 1st gear ratio of the ZF42 used in the IDI trucks and the 94-95 PSD's to be more useful. The problem is the torque rating of the trans is less than the ZF47 in the 96 and 97's. My question is what is really the difference? Anybody actually break a ZF42, or have any premature failures? I'd swap my 47 for a 42 in a minute if it didnt break. The first gear is actually useful to take off!