I spoke extensively with the guy from Promotion about a month ago, and yes they can do 26sp input shaft, cryo treated cluster gears, up grade syncro's etc....
IIRC price was around $2200 + core for the best of the best, plus a clutch, and they were also recommending the adjustable MacLeod slave cylinder to correct the missing stroke needed to operate most after market clutches out there properly. Total was up around 3 grand + core by the time it was all said and done.
Yet when you talk to D&D they say nobody is doing it, and that upgrade syncro's aren't even available.
I'll probably opt for the TR6060 for 4 grand. I just wish they'd hurry up and make it with a .50 6th gear. By the time I sent a core from Canada back to S. Florida I'd save 500 bucks to keep the 5 speed.