Which carburetor have you got your eye on?
Tons of intakes out there for slide carbs [Mikuni, Keihin, etc] and clone engines--so it's not entirely impossible to find something that matches the bolt holes on both ends [engine block and carb] and the right and I.D. That's a long shot though.
Otherwise, custom fabricate the manifold from steel tubing that is the same diameter as your intake port and weld two flanges on either end.
Like this video demonstrates--
https://www.youtube.com/watch?v=ixIyy4RCagM
To be honest though, seems like a questionable undertaking since there's no known performance upgrades for the engine that would make adding a slide carburetor worthwhile.