No luck with Wayback Machine, but in the meantime I thought to actually take measurements from my cab, and the T-nut holes already there are correctly spaced for the Faital Pro but not the Beyma - which suggests less hassle going with the former.
One option I'm wondering about though (and I guess this is relevant to BCCab builders too, so still on topic) is using an electronic crossover and bi-amping, rather than building the passive crossover - any thoughts? Would you expect any decent HF unit to give good results in that case, or would you stick with the Celestion?