I have heard of this set up of EFI cars before (90-96 Z) i was wondering what kind of advantage there is, how to set it up, and all the mods required. More Flow i guess is the big one. Kind interested.
I can't imagine how you could adapt dual throttle bodies to a Inline 6. You would have to have massive mods to accept the added air flow (ie. injectors, exhaust, intake.) All to take advantage of the added air flow. You would probably have to make a custom intake for it.
Now for a V-6 it would probably be easier, but you should post this in the 84-89 and 90-96 forums as most people don't bother transplanting a V-6 into the early cars. If you are going to do it you might as well go with the chevy V-8.
I have SIX throttle bodies on my inline six. (Three 45MM TWM Twin-Bore Throttle Bodies, actually). TWM also sells an SU Throttle Body, so adapting it would simply entail putting on an early SU Manifold and adding some 720CC injectors.
(On the 45's we use six 37# injectors, so with the twin SU's, if they accept a dual injector setup, 420CC injectors should be fine)