As one dumbo to another I know just enough to know there is a bit more to cross-over design than that. Are you thinking of using the T27's as "super tweeters" or are they going to share the frequency band with the HF1300's. It so happens, I know the last 2 Andrews to head up research and product development at Kef (I trained at karate with one, and the other is the twin brother of my "guru" as you call him)
And the boy Khoubesserian has designed speakers - the Ventrical and at least a couple of Gales. Would you like me to make enquiries on your behalf? If so, PM me as much relevant information as possible. (Although I fear their answer will be akin to my cartridge loading question, and is going to involve a microphone, and spectrum analyser)
Best of British mate