I did the search and found more than wanted! but I was left

I found people using 675, 680 and 685's
I also read that you add 3/4" per each pound of boost added, So 4lbs would be 3" and make the belt a 690 if the stock belt is a 660.

Thanks

 

I think it depends on what pulley you are using as some are different measurements than the others. I can tell you this, a 68.5 is way to big, I would do the 67.5 gatorback and be done with it.