I'm also very interested in this swap, specially because I'm in Europe where there is an abundance of BMW boxes.
But one look at bmw ratio's, and it's pretty clear most of them are way too short for our diff ratio's. I've already got the lowest diff ratio at 3.69.
The stock SR 5 speed ratio is at 3.32, 1.9, 1.3, 1.0, 0.76
The lowest ratio manual box (E90/E92 335i) is at 4.0, 2.4, 1.6, 1.2, 1.0 , 0.85 (source
http://www.bokchoys.com/differential/GearRatios.htm), but i'm not sure if that's still an M50-M57 gearbox..
And the E46 M3 6 spd starting at 4.2 is waaay too short... Mine is still a street car after all, and I'd hate to be doing 60mph at 3500rpm
Though I'm in Europe, i think it's still not easy to come by an M3 manual box, as it's going to have the "M" price tag attached to it...
Just sharing some of my thoughts.
Other than that, the fit seems pretty good and it's relatively easy to get the shifter in the right position. All conversions need custom driveshafts, but that's probably the easier part of the conversion. I guess those going after this conversion are for mostly for drifting purposes?
Edit: i had the damn ratio's mixed up, auto have way lower gearratio's