I actully saw these in action one time at a ride me and the wife went to. Was the dumbest thing I ever saw, but it worked pretty well. Dude was covered in mud and was never stuck. He had them on a stock motor and it would spin the crap out of them.
The post on the inside of the clutch cover actually holds the shift shaft against the shift star. It is probably worn and will not hold, so it will probably happen again.
One of my race buddies runs stock cylinders, stock stroke,stock bore, and it has been 4.50 in 300ft. first time out and 6.90's in 1/8 mile 2nd time out. He has been having tranny issues so may still have a little more in it.
I checked mine when I got home and they were at 260 when I ran them. Had the same setup as you Are running. I live in north Texas and I think I am about 400 to 500 Elevation. Hope that helps.
There is a 300 ft sand drag in Atoka,Ok. We are going this weekend. There are usually a lot of bikes there , maybe 40 or 50??? That's going to be like 6 hrs for you, but it's a good track with lots of good people!