If the the air chamber boots are as hard as it sounds, you'll need to heat them up (I use very hot water) and get them to fit the carbs first (with the carbs off the engine). Then let them cool in place, that way they'll keep their shape after you pull them off.
I pull the air duct (oval silver tube) out of the airbox, it'll give ya that extra bit of room to slide the air chamber in (from the right side, battery side) and then push the boots (use a little lubricant) over the carb openings, then tighten the clamps. Then reinstall the airduct (a little lubricant again) and tighten its clamps. It's still a tight fit, but not nearly so, its an acquired skill. In the future you may want to not leave the air chamber unattached to the carbs if your going to leave the carbs off the bike for any extended period of time.
