And reportedly the bigger unit from GA14I/GA16I is similar and a near bolt-on too. From circa 1990 Sentra/Pulsar

So, here is a crazy idea, since you mention that you are better at software solutions than hardware solutions. Use the SU manifold, get two of the 4 Hayabusa throttle bodies (43mm each), have one of your "hardware" savvy friends help you make an adapter for them to mount to the SU manifold, plug the injector bosses on each throttle body and operate the throttle butterfly. Machine the inlet runners for injectors and get a couple of feet of this; http://www.atpturbo.com/mm5/merchant. ... FUL-010&Category_Code=FUL and you should be able to tune up the fuel injection and make some good gains.

That pulsar throttle body looks fantastic. I'll see if there are any in the local wrecker's.
So is there any reason a single-point-injected throttle body would have to be downdraft? Since it's a pressure system I could mount it sideways. (I am extremely low on head room: there's like 3mm between the hood and the oil filler on the front of the valve cover.)

I've thought about quad throttle bodies from motorcycles. They're, by all accounts, a bear to synchronize even when it's just getting the butterflies aligned with each other.
That's one reason the single point injection seems attractive: less stuff to go wrong.

Good point on the synchronization. I just figured that would look pretty cool and since you mention clearance might even address that. I don't know of anyone ever trying to mount a "downdraft" style throttle body horizontally but it seems like it should work.

Camquest have software allowing you to choose your cam, Part of that software also includes carburettor sizing and more often than not the recommended size is smaller than what people use, I would like to think they know what they are talking about when it comes to carb or throttle body sizing too many people go too big in that department.

Too big means poor throttle response lousy fuel economy and often less power, Do the research

http://www.camquest.com/