Gearbox Upgrade - Help Needed Please :)

Hi all,

I drive a Nov-2001 Mini One.

...so a few backs, I had a leaky battery (from GSF's own brand rubbish) which resulted in my gear linkage falling apart from the top of the box.

After fixing that, its come to my attention that the Clutch is now not as good as it used to be and there is often a noticeable lag in speed change when accelerating.

I spoke to the local dealership and they have quoted me silly money for a clutch change.

I looked around and have read that it is possible to upgrade the gearbox from the midland unreliable unit to a 6 speed one from a newer model vehicle which is stronger and improves drivability.

I understand that apart from the box, I'd need the driveshafts and linkage upgrade as well, but which models can be donors for this?

My question is, are there specialists out there that can do this and what sort of money does it cost to have this done.

My thinking is that if I'm going to spend £600 at the main dealer changing the clutch, I might as well spend a little more at an independent and go for an all out upgrade.
It's worth noting that there is nothing wrong with the current gearbox and the car has only covered about 63k miles.

Any help would be greatly received :)

Thanks