you asked if carbed cars could be installed with SGI. The answer is yes but the technology may have to be assembled from various suppliers and will require a "stand-alone" ECU with programmable firmware.
Also the resulting installation will only approximate (in some cases) exceed the original petrol performance if the engine itself is modified to work as dedicated system.
I am currently assembling such a system and will begin installing on my 1985 MB 200 W123 sedan probably by next month.
Actually if you already have a venturi kit installed -- the boot end (tank multivalve and vapor box) remains the same and usable.
The "front-end" will need a new regulator, fuel rail, and the vapor injectors tapped directly into the manifold. Its probably wise to get the front end as a set. Prins of the Netherlands has the best injectors which are OEM from Keihin of Japan, makers of injectors to major manufacturers.