If the HF shaft is too long, just grind the output shaft to the desired length.  Don't put too much side/end load on it when grinding, and toss a plastic bag over the motor to keep the debris out.  Be easier/more stable than creating shims, and might look nicer.  Just a thought. 
PM me on the break in procedure for that motor if you want.
	
		
			
		
		
	
				
			PM me on the break in procedure for that motor if you want.
	
	
			
 Great motors, I have one on a clone class racing kart thats pushing out about 13 HP, not bad for a $90 engine from HF.