From my experience, in order to get the Aluminum pulley you are looking for, you will need to either retro-fit older 747 style diff and track down the 40t Serpent pulley or modify the car with a custom rear pulley (I run 10mm belt in high power drag car). This is not difficult if you have access to shop tools and some skills (if not I can put you in touch with someone that can perform this for you). I would recommend a mod1 upgrade too if your serious about going fast. These are just my opinions and definitely not shared by all ;-) btw this Pete? I think I have an 18t on the way for you lol