I have many cars come through my shop that have been stored for many years and run into alot of overheating problems ,first thing Id do as one of the other suggestions is knock out the rear freeze plugs and get inside there with a heavy bent wire I have had times when the build up of sediment is hard out behind the freeze plug to the piont where it has to have a chizel knock a hole through it but the sediment always collects in the back , this must also be done before you even think of spending any money on the radiator as if this is the problem and you do the radiator ,you'll be doing it again in a short period of time as when it does break loose it has to lodge somewhere and that clean radiator tube is the new resting place . you could have a local smog guy stick his sniffer in the top tank that will tell you quickly of a blown headgasket ,which is not uncommon with cars that have been sitting as it only takes a little corrosion in the headgasket area to create blown gasket that will cause it to get hot in the time you are talking ,you can also buy a test kit from auto parts store that you fill a tube u and hold in the top tank and it will change colour if there are exhuast gases in the system, flow in the radiator is easily checked by leaving cap of and giving it a couple of rev's and watch water flow ,also I believe that the thunderbird doesnt have any mechanical advance inside the distributor so if your vacuum diaphragm is out you will have no advance happening, this is easy to check with a timing light also.
