That 200hp rating is "net hp", rated with all accessories hooked up and a full stock factory exhaust system attached. Just freeing up the exhaust system ought to make a noticeable difference, but I don't see 350hp with the stock 350-sized TBI.
You should be able to make it with the bigger 454 injector body, which was adapted to a factory 4-bbl carb intake manifold by GM, but you'd still need more mods than that to get 350hp.
Some head mods, better yet new heads, and a cam change, and by now your computer's liable to be so confused it'd have to be modified to function with all the other stuff you changed.
It'd make a hell of a sleeper motor, though, once you got it all sorted out.