You want to look at a keyboardio model 01 with Matias switches. Split board, just bolt them together with a rod if that's a problem. Not dishes, but as tented as you could want.
I think one of the Dactyl case printer guys might offer an Matias hole option, but can't remember. Again, you'd have to attach the two cases to the same baseboard. Though frankly if you're going concave already, split vs one piece is an odd thing to be worrying about, especially as tenting is one of he key points to these designs.
Maybe look at Malton, I can't remember what switches they use.
Alps is kinda feasible. Retrofitting buckling spring, forget about it. The switches don't work that way.