With a child that close to the height requirement I would not tell the child that they can ride the 40" attractions. At each attraction I would say, "Let's see if you're tall enough for this one today". You really don't want to have a kid all psyched up that they'll be able to ride something and then be turned away when he gets there.
My youngest made it on some of the 40" rides this trip, but was turned away three times. He never rode Test Track. Twice he was told that he was tall enough outside, but when we got to the stick inside they couldn't decide if he was tall enough and had to call someone else over who decided he was too short after several minutes of trying to push their hand between his head and the stick. It was very embarrassing and disappointing. One day he rode Soarin, but the next morning he was too short. He rode BTMRR at least 15 times.