my understanding is that the crossfire unit would probably be a reasonable substitute but is a slightly different design, one difference is that the pnc50-bb (original) wasn't intended as a flyable device so you wouldn't be able to fit an engine through it. however your measurements confirm what I gleaned from the rocsim file, I just have to wait for the parts to arrive so I can build a few motor mounts(this bird, alpha, and one to be revealed later). thanks much for doing the measuring.
Rex