I have been (slowly) working on a TBI system for my 250. There has been quite a bit of discussion over at
Inliners.org on this topic, several people there are doing it.
DIY-EFI web page has a lot of info on customizing GM fuel injection systems. Once I have my TBI setup done (hopefully this summer), I plan to put together a tech page.
The TBI will still have the carburetor fuel mix quirks, but it should be far more efficent, and at least a bit more powerful than a carb. The most difficult part is going to be tinkering with the engine computer programming. The injectors for a 4.3L V6 should be just about right for a 250 (4.1L) and 305 injectors should be good for a 292.
Port injection should also be possible, but I couldn't think of a way to work with the siamesed intake ports.
