[Purdy Swoft]

I'm not sure how much experience that nyou have and this is a long shot but could save you some hard work. An exhaust leak can make a clicking sound. With the engine cold, remove the fan belt. Start the engine and quickly before the manifold gets real hot ,feel around for leaks between the manifold and block and at the connection of the head pipe to the manifold. With the fan belt removed and the fan not blowing air, an exhaust leak can be easily found. you can rev the engine at the carb with one hand while the other hand feels for leaks. I've seen a clicking sound caused by a leaking manifold gasket fool people that I would have thought would have known better. This may be the best hope. Otherwise it could be wear at the center cam bearing causing the camshaft to rattle in the block or the center mauin bearing.