If the clutch is the only beef you have the with the GP460, then get the better clutch springs that you'll HAVE to get a month or so down the road. Just replace the springs up front!! I'm just not a fan of the twin motor idea, but to each their own.
29'er + 47R + shift kit + Nuvinci hub = "the ultimate"
I guarantee you that such a build would beat any Thing else. PERIOD.
In terms of acceleration [up hills], top speed, weight, balance, etc.
It seems that the shift kit is the only way for the Nuvinci to freewheel without the Staton gearbox. Staton gearbox is just too heavy for me.
But yea... it sounds like you've already got it all set up, you just haven't put the wheel on the bike. Try that out for me and let me know how awesome it is!!
I have tried various aftermarket clutch springs on the 460 engine. I also replaced the its clutch with a velvet-smooth pocketbike clutch.
They all failed within a few months.
Granted, it could've been because of the steep learning curve of using this engine. It could've also have been because I expected the engine to pull away from a standing start. It could've been because of using a 32t first gear, instead of a 34t. This engine's clutch springs failed with friction drive AND shift kit.
On my last clutch spring failure in its center-mount position and shift kit, I decided to pull the 460, replacing it with a new Tanaka 47R engine. It was a good choice. Even though the 47R might have less power, it gets the job done on my commute. In its center-mount position, its expansion pipe wraps perfectly around the top tube. In eight months running, the Tanaka has not experienced any clutch issues or ANY problems whatsoever. The 47R is considered a loud engine, but it's much quieter with a pipe. It also gets about 80mpg, accelerates very well and cruises easily @ 35mph. If pushed, it will maintain 40mph and peak past 45mph. AND, it is a very dependable engine.
IMO, Tanaka 47R is the BEST high-performance engine for use with a shift kit and cassette gearing. It would work well with a 26" OR a 29er. Cassette gears should be a better choice than the NV hub. They are more than 10 times cheaper, MUCH lighter and easy to replace. In a center-mount position, the bike is better balanced than a rear-mount setup, ESPECIALLY if fitted w/a cassette. With an NV hub, it becomes tail-heavy, I would imagine.
Staton gearbox isn't really that heavy. Engine power nullifies extra weight. My Trek w/Mits TLE 143 engine, Staton box and NV hub weighs 62lbs., the same as my Diamondback bike w/center-mount Tanaka engine. The Trek's front end is EXTREMELY light; the Diamondback is almost perfectly balanced w/its 29" ROCKSHOX fork. Methinks that extra weight needs to be added to the Trek's front end. It seems too easy to jerk the front end off the ground and flip over backwards.
As mentioned before, I have two 29er frames. One will run twin 460's, just for the heck of it. The other will run a spare 47R with shift kit and 11t-34t cassette. for the 29er w/shift kit, I'm trying to get a vendor to fab an 80-tooth 8mm chainring sprocket. This would lower first gear from 37.09:1 to 41.2:1 to compensate for the taller 29" tires. Eighth gear would be more usable @ 13.33:1, instead of 12:1.
I wish I could center-mount the Staton twin-engine gearbox. The bike would be better balanced than a rear-engine setup. With too much weight on the tail end, I just might HAVE to center-mount the twin-460's.