No need to fit a 12" fighting butt, Nigel, there's already 14" of extended handle / fighting butt below the reel seat on my 13ft Fladen Maxximus, and I suspect that would go for most similar rods.
Whilst measuring this I've also just noticed that the butt cap has fallen out during storage

- and it's clear that it would be easy to cut however many inches off the handle to make it a more comfortable length, and then reinsert the butt cap. (Yeah yeah,

again!)
One other thing: the upper rings on the blank are very small, being made only for mono, so you might get quite a lot of resistance to a fly line. But I'm sure Steve Parton could whip on a set of suitable Fujis, no problem at all?
Theo