I find it best to leave the rubber air inlets completely off; then mount the carbs to the engine cyl.hd. alloy inlets first.
Soak the ruber inlets in a jug of hot/boiling water to soften them (at this time of year), then with either cyl 2 or 3 first, carefully scrunch the rubber intake and 'just manipulate' it over the carb intake throat, then onto the air filter manifold box.
It is very 'fiddly' but you will develop the technique.
Sometimes having a BLUNT screw driver or narrow spatulata often helps.
Good luck
Oh and on completion.....apply bandaids to knuckles!
(I'm sure there's over threads on this on here somewhere if you search.)