airbox to carb? tight is right! if they are new and never been installed, its always a tight fit. just a light wipe of premix from the tank will usually make them slip right on.
supple, never. overly rigid is usually a sign of typical aging rubber. unless they were exposed to some severe elements, i have never seen one really go bad on the newer sleds short of a tear. (newer meaning after about 97), unless they came from the midwest or right coast.
depending on what they actually came off of or if your carbs are stock or not, remember the 600 sleds in triple format ran a slightly smaller carb.
i may have an extra set of boots laying around that are actually from the 700 triple with 33mm carbs. if you have a way to accurately measure we can compare or they can be available cheap if you need them.
just make darn sure they are completely wrapped around the carb and properly oriented into the airbox if you choose to rune what you have.