Maybe somebody already mentioned this, but when putting the center pin through a tapered piece, you should have the mating surface square to the opposite (spring) side, not square to the perch side. You can get a tapered sleeve/washer to accomplish this, but it seems like the fewer pieces involved here the better.
I thought somebody was offering tapered zero rates. They would come with the center pin seat machined to the angle of the opposite side and would satisfy all of these conditions at once.