Have been looking into the conversion a bit more and people are generally saying that the VAG boxes are heavy and dont have a nice change.
So im considering a PG1 B4BPQ box instead now, from a lotus exige, or some similar rover derivative of it (the exige one has a quaiffe as standard so would be the ideal starting point)
Martin Hadland on here (reyland motorsport) does a very neat conversion that allows it to be fitted trivially to the engine, and means you can run the equal length shaft kit from the rover too.
Looks like a reasonable way of getting a reasoanably light (36KG apparently) and fairly strong gearbox with a good choice of ratios and a good choice of diff options into my car.
Will keep looking into other options as well though, so this isnt meant to be a final decision, but figured its worth recording stuff like this in case it interests anyone else on here.
He also gave me this stark warning about why not to use the standard rods, this is from a 260bhp engine that didnt even have a raised rev limit:
