Originally Posted by Stretch

I'm interested in this too...

...but I've been wondering about actually doing it in reality - the biggest problem I see is how you would fit an over drive onto the rear casing of another transmission. The lengthening of the output shaft shouldn't be too difficult - but looking at the Haynes manual (yes yes I know it is crap) section on the manual transmission it looks like the clearances for the rest of the gearbox come off the back cover.

{Much like the rear end of the 722.1 automatic transmissions - get that nut on the output shaft wrong / position of the back end of the gear box wrong and everything else will be out of whack; gearbox not last long with bits in wrong place}