121 to 136 what tooth count to change?

I am long tracking my 98 mzx 670 to a 136" and a 1.5" lug track. Has anyone been down this road???...... what gear changes if any did you find worked the best, or did you have to do any clutching????? Any other tips would be great.

Drive sprocket...should I drop down to an 7 or 8 tooth?
Do they make anti rachet sprockets with a 7 or 8 tooth?
Drop a drive sprocket tooth , then have to make a gear change for correct gear ratio?

cheers,
Jim