i did see somewhere, ebay i think. someone took a 302 with a tpi and put a turbo on it, looked sortof stock, other than the engine being longer and the manifold looked wrong.
i think it would be kind of cool to see someone do it, with a turbo that is. lets face it, the 231 are not powerfull motors without the turbo, don't belive me? disconnect the wasgate arm and go for a spin, it sucks. and your still getting some effect of the turbo still. take a sbc and it runs pretty good to start with, in theory it would run amazingly well with the same turbo setup.
or this might be an example of why to keep the v6 and just be happy with it.
one thing i do what to know. i'm guessing your going for a fast car, why use a buick for that? they weigh a ton and have the aerodynamics of a brick. if you are going for the looks then all is understood.