On my 97XC600 I dropped the sproket & put on a modified Helix. Both of these helped off the line but dindn't help out the top end (as you can imagine). It was studded (144) & I had the weight transfer about maxed out - it was pretty decent off the line but alas it ended up being no match.
After all that work my new stock 700 was 5x that 97. I'd recommend saving your $$ to get a new US built motor - it's night & day.