I don't have the spur yet, but as far as I know I don't need to make any mods except maybe to my gear cover.
Current gears are:
Robinson Racing 87T 48P Spur -
http://www.amain.com/product_info.ph...-Spur-Gear-87T
Robinson Racing 23T 48P Pinion -
http://www.amain.com/product_info.ph...inion-Gear-23T