I had to deal with this problem last year on a customers new engine. He wanted an Indy cast alum cover. First problem was his ATI balancer wouldn't fit (balancer hit the cover). We got the correct offset ATI balancer, then the cam button set out too far (the cover would not reach the block). I had gotten a real nice cam button that I wanted to use from Todd Marsh (I think it was a Diamond brand, 3 bolt cam retainer & button combo, w/ inverted torx head bolts. Real nice part). I elected to machine the face of the cam gear approx .025" to get the clearance that I needed. Worked out fine, but this was WAY harder that it needed to be. Brand X has many different options that just bolt on.
Also, on a different customers RB engine this year, I used a teflon button (made by Comp Cams) and a Milodon steel cover. I had to file the button to fit, not hard, but time consuming..
This really shouldn't be this difficult.

Brian