Gearbox swap options for 5spd 2001 M750

[The Mad King Pepe']

Pretty much as the title says, I have a 2001 5spd M750 (carb'ed) and I'd like to swap in a 6 speed gearbox.

I've seen a few on eBay, but before I throw any money at it, I figured I'd post here for some hints/suggestions.

My questions are:

• will a 6 speed fit in my gear box?
• what will I need to change aside from the gears? drum? bearings?
• which would be the best candidate for a transplant? I think the gears from a 620 would be too short, while a 900 would be too long, although that could be managed with different sprocket sizes...

I have thought about swapping the whole engine, it would certainly be faster and perhaps cheaper but that's not what I'm interested in doing. I'm thinking of this as a winter project, an excuse to open up the engine and possibly learn a little more about how it's made.

[caperix]

I think the only drop in 6 speeds will be from the small case motors; 620, 695, 696, 800.  They should all mate up to your clutch so I think as long as you get the trans, forks, & drums you should be good to go.  Those with more experiance should be able to add more info.