I'm sure it can be done, but it will cost quite a bit. Why would you want to do that? You would probably be better off just trading in the truck for one that has an allison. I haven't read of many people doing this conversion...actually I haven't read of anyone doing it. Most people buy the ZF-6 for a reason.
Well, you still need to buy a TCM, the column shifter, and associated wiring harnesses. Does the allison come with the torque converter? I hardly think that you can get an allison that doesn't need a rebuild for less than buying a clutch....how much are you looking at spending on a clutch? I think all being said and done, it will be cheaper to change the clutch than to get everything needed for the conversion.
I think i have 1800 bucks in my clutch setup, much cheper than even a good stock ally let alone one that will hold big power!! I say the conversion could be done but you probally would need something like a wrecked parts donar truck to make sure you had all the right peices and parts !