That is the same engine I am using for my yerf. It has a reputation of being bullet proof but not the most powerful, stock is around 13hp/11ft-lbs. You can replace the dish factory piston with one from the ATC 200x(flat top) and jump from 7.8:1 to 9.6:1. I approximate mine should put down around 15hp. The centrifugal clutch inside is the weak link when adding more power, the trike guys estimate it should hold up to around 16-18hp.
The sprocket issue can be cured via jackshaft. Not pretty, but effective. My worry has been the weight increase on the clutches, so I added HD clutch springs for the plate/shift clutch, and deglazed the cent clutch bell While I had it apart. The springs will make the shifter harder to move, but it is a compromise I was willing to make. I would advise to dump the stock CDI, as they are troublesome and expensive to replace. PM me if you get it, and we will talk more about things. I personally like the engine, and the 5 speed trans should be great. The main drawback, no reverse
