Most all motorcycle engines/transmissions are very similiar in overall design.
If you can read a micrometer and a service manual, it's not difficult at all to rebuild one.
The thing about PowerHouse and people like them, is that they have alot of experience with alot of bikes, and more importantly, know which part combinations work best with what engine.
When you buy your parts from someone like that, you know you're getting high quality and knowledge to back it up. As well as a Good dyno tune to finish it right, which we know is a must.
As far as assembling things, it's not difficult if you take your time, measure and torque everything.
Unfortunately, too many people want to throw something together, then take it to a reputable shop to fix their screw ups.