If you get the new alloy motormount
http://os.3racing.hk/products.php?products_key=5208 you have even more room for bigger pinions.
It also lowers the motor by about 1 mm.
It also lets you flip the belts to the opposite side for better weight balance.
If you do this widen the holes for where the diff pulleys are.
Only sad thing about this mod is that you need the Sakura Zero soft top deck.
If you use spur 65,pinion 40 and a FDR of 2 then you come up to the same FDR of 3.25 so i don't see a problem there if you don't want to buy the spurgear adaptor with 19teeth pulley
regards Roy