6 speed would be nice... you should be able to adapt whatever you want to fit, space will be an issue because its pretty squeezy in there already. so if the box your looking to put in is larger, youll have to modify the tunnel there. i know when my old man had to modify his EH ($45k+ spent, 16yr build time... thats dedication!) to fit an ecotech six an box, it involved cuttin through a chassis strength section, and then as a result needed engineering certification. dont think have the same issue with the VL though... easier an cheaper to jus rebuild the 5spd an whack that back in there, unless you dead keen on the six.
If you mainly doin city drivin though youll end up with one leg bigger then the other from pushin the clutch so bloody much :rofl: