That looks like an ugly amount of work!!! I think I said earlier, the flat head bolts I got didn't seem to match the angle of my countersink. Had to putz around with it and a large bore drill bit to get it to set well and deep into the phenolic I showed earlier. I will say my countersinks had a hard time chewing into the phenolic, steel would be down right ugly.
Build up the limb butt with phenolic or fiberglass with some wood of choice thrown in for looks......or buy the washers! Don't know where else to get them but from Binghams. Or as mentioned above, McMaster-Carr. Let me know if anyone finds them elsewhere. Till then, I like my limbbutts. Will probably use thinner phenolic next time - but my limb mounting system survived a bad dryfire when the riser didn't so they must work okay.