how can you be sure that you head gasket is gone before you strip it down? mine is losing coolant but no leaks and overheats, and the coolant smells like exhaust gasses and no sweet like it should,

If the coolant smells like exhaust gasses and your loosing coolant mysteriously you probably have a HG failure.

You can compression test it and see which cylinder is leaking.

if your taking a head off you may as well take both off in order to re-grind valve seats and replace valve seals.. Check cylinder head mating surfaces for warpage as this may be why the gasket failed. If you want to get carried away you can also replace all bearings and seals inside...