OFFSET: 3/4" of an inch AIR GAP will get you reasonably close
TWIST: Check front and rear of the secondary to see how much engine "TWIST" there is
CENTER to CENTER: Also, remove both clutches and BUTT an accurate metal rule up to the jack-shaft and eyeball Crankshaft Center and look for 11.00" (11.5" is C/C and the jack-shaft is 1" Diameter)
I have pics posted in the INCREASING your IQ at the top of this section