I am also using a plate on top of the spring pack. Mine may be from Dirtbound.
What I think that sort of plate design needs is a brace running down to the axle for support. I understand why they are not sold with such an item--there are too many variables in spring pack thickness. But with Dallas' shop at your disposal that should be easy to overcome.
Up above I am using an aftermarket polyurethane bumpstop, the sort that looks like it has a large "U" cut out of the middle of it. That gives a somewhat progressive stop.
That said, given the level of everything else on this build, I expect to see some fancy Fox/King air-bumps as your final answer.