I would NOT get an adjustable if it were me.
This is just personal preference though.
Correctly speaking - the adjustable ones are truly the proportioning valves.
The fixed ones that you can buy are called combination valves. Proportioning valve is just the "generic" name for all of them.
I'd just pick up a disc/drum combination (proportioning) valve from any vendor. I think Mike's Bump and Grind Garage is about the cheapest. He also has aluminum.
http://estore.websitepros.com/126980...-GM/Detail.bok
He's a board supporter/vendor.
That's where I got mine - and all the vendors buy them from the same supplier.
DLB
DLB