oh no, alcohol in the fuel is going to dissolve your alcohol proof gasket materials!
hang on... no they wont.
leave the gaskets alone.
leave the twin carbs alone. only one bike i know of ever had two carbs on one cylinder and it had a reason for it. good old honda XR 200, if it had just one BIG carb, of the same total area...it would die when the throttle was opened wide too fast. no air speed through the venturi, no fuel gets sucked up and mixed with air, engine dies.
being on one cylinder, they did not require synching. one carb was "untuneable" one wasnt. both throttles were locked together, with no adjustment necessary. or even possible, from memory.
then someone developed the CV carb and the twin carb concept was thrown out on the rubbish heap where it belonged. no matter how fast or wide you open a CV carb, its slide will only lift as high as the engine requires.
adding a bigger carb is going to do nothing for performance unless you have opened all the ports up to suit the increased breathing capabilities. if the hole behind the carb is only 16mm across, sticking a 20mm carb on is going to do what? somehow squeeze extra air down the 16mm hole? reality says no, it wont.
but, some people wont listen to logic, its your money, so if you think two carbs is going to make a huge difference, and want to stuff around with different fuels that also make no difference... go for it
now, if you were running straight methanol and needed one carb setup for the extra fuel flow...maybe. easy way to get double the power. buying drums of methanol isnt exactly cheap when youre using four times the amount of fuel! definitely not the way to proceed if mileage and economy is your desired outcome.
