I had thought the biggest hurdle to doing anything with TBI is tuning it. Regardless, as a seasoned engineer I place greatest stock with things that are guaranteed to work and many of your options seem complicated, uncertain of success, expensive, and will take a great deal of time to accomplish leading to an ever-common abandoned project/went a different way posting for parts-for-sale. I would whittle down to three:
(1) Head replacement. Either after-market TBI or vortec heads with a carb manifold and TBI adapter. Unsure which would produce better results but vortec heads are cheap (more than $300/pair and you are overpaying) as are carb manifolds and TBI adapters for them. Much cheaper than a TBI vortec manifold. And compare to after-market TBI heads. Either would give an immediate noticeable boost for moderate cost over a weekend of work. See if you can live with the truck then. If not:
(2) Gather funds for an LS swap then sell your truck and buy a Gen 3 with a 6.0 already in it and see if you can live with it. If not:
(3) Supercharge (2) with not hard-to-find kits and see if you can live with it. If not mortgage your house, sell your wife and children into slavery, borrow money from the mob, and then, maybe, you'll have enough to buy a gen 6 truck.
I understand the allure of GMT400s. I have a 1998 Z71 k1500 that I have put more work into than most would deem rational (marine intake and cam, cpc, 4L80e, shorties with HD exhaust upgrade, plus a few lessers) but I was starting from a better platform than you have. Honestly swapping a TBI to an LS vice just swapping trucks isn't something that is sensible unless you are doing it for the sake of doing it (which I can understand).