I agree with PeterC.
@Gsxr1100er: From pics carbs are the same of BST 36 installed on my 1990 GSX750F. The Venturi passage (air filter side) on GSXR are round. These carbs have an almost elliptical shape instead. The only thing that i see different is the choke command: on my there' a cable attach, on these there's a knob.
More, the tube in brass you can see here is the passage to enrich the mixture at cold start.
:
If this carbs was coming from an usual GSXR750, the tube was on left, with a different form and function: for the GSXR is not cold enrichment, but Hi-RPM enrichment, in other words a Power Jet.
Maybe, but it's just a guess, this is the method used to restrict the power on Swiss models: installing a 36 mm carb instead a 38 mm...