I was wondering if the main differences between the 1996 Summit 670 and a 1999 Summit X 670 are the cylinder porting and heads? I own a '96 and was given a 1999 with low compression that I'm thinking about rebuilding. I'm wondering if it would be worth putting the head/cylinders and possibly magneto/flywheel on my lower end to gain the hp or just swap motors? Is it a noticeable upgrade?