My first Kitfox, a model 3, had one of the earliest Rotax 912 engines.

While it did not have a dual throttle handle, it did have a pivot bar behind the panel that had two thin throttle cables coming off each end of the bar going through the firewall to operate each individual carburetor. It worked but required
more upkeep, more carb syncing and of course it had more failure points. I soon removed it for a much simpler safer heavier duty split throttle cable that gave me a direct connection to the carbs as used on the later model fours. Much better and simpler system.