Like /\ said. Clippard makes the valve body. sold and used them for years. Fastrax has all my stock.
Brad (1200psi) sells them as well.
Highly recommend them if you run a carb and you understand fueling. Way easier than changing jets.
Start out with about 3-4 sizes SMALLER than normal main jets. simple set up, after you have them installed, open them up (full fuel) and run is slowly up to WOT. You will notice when they kick in cuz it will fall on it's face and blubber. 1/4 turn at a time, turn them down until it is clean. At this point you are still on the fat side and way safe. If you do this down low, as you gain altitude it will start to blubber at that same throttle opening point. Adjust accordingly. Once you are at your play area, just do some plug and piston was checks to get her perfect. Unless you are like me, once she runs good and motor is happy with a little extra fuel, no worries on long pulls. Make good notes for each area you go.