I'm curious about this too, as I know the GM TBI will be cheaper to do, but it's also more of a pain to tune. I'm sure somebody makes a program so you can use a modern computer for tuning it, right? The computer we used on the '88 TBI finally gave up the ghost and I'm not sure what to use instead. What're you using as a chip to start with? And I'm guessing you plan to tune it after that?
Is your plan still to use the 454 adapter to the 4-barrel manifold? I know the 2- and 4- barrels are both dual plane for these unless you get the Stage 3 intake from T/A, but the TBI can still theoretically take advantage of the dual-plane setup. And I know the 4-barrel manifold on the Buicks is just a much better design than the 2; the 2 is a weird shape and the Quadrajet isn't the only reason the 4-barrel makes so much more power/gets better mileage...
Thanks for the info Herk.