The boots are supposed to be tight, as they hold up the head-side end of the carb bank. But it's not impossible. Unless you're using a pry bar or large rock to get them out, you most likely won't break anything. Just make as much room as you can (which you did already), grasp the sides of the carb back with both hands, and rock it up and down. Eventually, you'll be able to rotate them down, and then off to the side. You can do it (from The Waterboy).
One more thing to try/help:
VERY hot water on the boots between the carbs and the head, may make the rubber supple enough to free things up. I almost suggested using a heat gun, but too much heat in that area, especially with gas around, may not be a good idea. Also, burnt boots might be expensive to replace.
Hmm...Burnt Boots...sounds like a band name.
Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.