A LOUD ticking noise is usually an exhaust leak. I don't know much abotu the gasburning Scouts, so I can't say where exactly to go, but a god bet is to just try to locate where the sound's coming from (I'd guess one of the exhaust manifolds) and replace the gasket there. Again, just an idea...good luck!
i would be it is a lifter ticking. espically if the engin has lots of miles. try taking a quart of auto tranny flid and dumping it in to the engin. it will mik with the oil and "clean out" the carbon in the engin. run it this way for about 50 miles or so then change the oil and see if the clicking noise is gone.
if it is an exahust noise it would be where the exaust pipe bolts to the exast manifold. just tighten them up.
Take a piece of vacuum hose,stick one end in your ear and poke the other end around the exhaust manifolds to try and find the leak.
I've owned three scouts and had to replace the exhaust manifold gaskets and donuts on all of them. However they will still leak unless you
have the manifolds machined to provide a smooth mating surface to the heads.