Hello...I'm Dr. Coldiron and I will attempt to help you with your veterinary question! Have you considered radioactive iodine therapy to treat the hyperthyroid issue? It rids you of giving pills twice a day and is relatively safe. As for the hard distended belly, your cat wouldn't likely be very content if he were blocked. Usually they are very painful when blocked. Because of his age and history, it is probably a good idea to get him to your vet so that they can at least feel of his belly and see if he is constipated, has a mass, a blockage, etc. The only real way to know is to have a doctor palpate the abdomen and possibly take a few radiographs. You may want to divide his food up into smaller portions and feed it more frequently throughout the day. You could also give him some Laxatone (or other hairball ointment) to see if this helps him. If you are really concerned though, time is of the essence when dealing with gastric issues such as blockages, so I would tell you to get him in to see the vet soon if you really suspect that this could be the problem.
No problem...let me know how things go!