Getting ready to change trans pulley on my 03' flhri to a 30 tooth . Stock 88 motor could use some help with the Frankenstein conversion .I'm assuming the stock 139 tooth belt will be to long,and I'll not have enough adjustment available. Is there a formula to figure belt length ? Would reducing belt teeth by 2:1 per tooth reduction of pulley teeth work ? Got all the new seals , new pulley and tools to make the swap and would like to have the correct belt on hand to avoid reassembly delays.