You can use a whole bunch of different types of transmission fluids.
Belray is a 90W "gear oil", it's just specified for use with wet clutches.
ATF is about $3 a quart and works great too. It up to you about how much you want to spend on keeping your transmission happy.
A boyesen rad valve is a on piece intake manifold and reed valve assembly. It has a smaller throat diameter than a factory intake manifold for "greater velocity" for more low end torque. Super Noober runs one, he wasn't so impressed until he took a dremel and opened it up. Then it came alive. One thing the rad valve offers than none of the other do is only one sealing surface.
Moto tassinari V-Force 3 reeds are notorious for leaking at the gasket area because the frame is made from plastic and occasionally has casting issues with the sealing surface.
For a set of replacement reeds, however, they offer the greatest flow increase with a simple bolt on modification (which is why they are on everyone "must-do" list). There are other ways to get even more flow but not with the ability to simply switch back if you don't like them.