Done it...my advice though is not to go to big cc's...it won't lock up, i.e. ZERO traction...its just too much torque for that little weight(can't believe I just said that but its true)...I raced margay style chasis and a friend had the same with a cbr 600 f1 set-up and he had to do one sorry ass slow launch off the line(or a full lap around the round track) before he could punch it in second. First gear became useless except for burnouts...it would fly through first in about 2 seconds, then you had to shift to second and light it up about half way throught the powerband when it got traction...he then switched to a swap from a small 125cc yamaha and ran ten times as fast(well not top end...he tried to top end it repeatedly on the round track and just lost traction at HIGH dangerous speeds...once around 80mph and the rear right tire snapped off the axle like a twig from the side load in the turn due to the small 6mm bolts holding the rim to the hub)...the 125 out accellerated the 600 by FAR through out the powerband due to traction....and it cost less to buy/install than just the fabrication to make the 600 work(the frame had to be widened and stretched a little plus custom wiring harness/mounts/radiator/etc....)...check out http://out2win.com/catalog/index.html
He has real good prices on excellent shifter kart kits....