One of the problems with working with 30 year old bikes is working with 30 year old rubbers.  Note that said 30 year old rubbers tend to harden, and shrink, so they no longer fit right and are a pain in the nether parts to remove and reinstall.  One method of softening the hard rubber air boots that join the carburetors to the air box is to blow hot air on them with a hair dryer.  This will soften them, i.e. make them flexible, so they are easier to install.  Unfortunatley they only retain the flexibily while they are warm.  As they cool down while you are trying to install them they will stiffen up and be next to impossible to install without using the hair dryer outside and holding it with the 3rd arm and hand you had to grow through evolution just for this purpose.