I know the 85-86 had 22's on the rear and 21's on the front

I think the 88-92 models had 21's on the rear, not sure about the 87's since they coujld have some parts off the 85/86 or parts soon to be used on the 88-90 models, plus they had some 87 specific parts on them

Same general rules should apply that I recommended earlier.

2 strokes don't have alot of low-end, I prefer to give up some top-end speed to gain some low-end grunt by narrowing the ratio. Lets say stock is 71mph, I will sacrifice 2mph and settle for 69mph for a quicker quad.

http://www.dansmc.com/mc_software1.htm

plug the #'s into the chart, use 8,888rpm as a baseline to see for yourself