I was going to TIG weld it on but decided to opt out for another engine, the only reason was just in case I didn't get it rebuilt over the winter in time for spring. This way if it takes longer then expected I can still be riding the bike in the mean time.
As for the sprockets and the chain? As you can see in the picture they are quite new. I put a new front and rear sprocket and chain on last spring... roughly 1500 - 2000 km's ago.