I sent Mark a question via email and he got back to me the next day
They`re not GM components, they`re Howe Racing. They`re available in .10" increments. What height would you like? FWIW we spent a lot of time testing these and the +.50" you already have worked out best on all of our test cars.
Not the bolt-in type you have but the screw in (rebuildable).
Great service from him.
Cheers - JIm