I checked and yes the ZF8 gearbox is stronger than the ZF5 gearbox.
This is due to the power output of the engine, and has nothing to do with the differential ratio.
As my gearbox will still be connected to its current engine, this is a non-issue.
your car is an auto it always starts in 1st, which will work out were my second is if you change the diffs, all of the ratios are available if looked up, and the reason i used to start in second(not any more) is because my first is lower than...
pulling away in first is very relevant even when not towing your 1st gear will fall roughly were my 2nd gear is according to your figers and starting in second gear is what destroys the centre bearing on my prop, oh and ive not changed any mountings