Depends what type of carb you have - itd actually be easier with a walbro type ( OHV) then the flathead one piece carbs - i take it its for mud/water?
The walbro install could be as easy as making a steel flange and weld a elbow and stack on it - some sort of air cleaner should be installed so crud wont get sucked into the motor. Itd be easier to make a solid stack, because a flexible one would be too low.
The flathead 'one piecer' would need an adapter made to fit the bore of it before it can turn to the stack.
Ive run my 80's agway in mud/water for years with stock intake , BUT i havent been in water past the footrests tho , problem with that would be belts slipping , water getting in the trans, youd need to seal the electronics , seal/raise the oil fill ( or use a old style plastic plug).