If the water is not leaking out, and it's not in the tranny or engine oil, then it's going out the exhaust. I would start and let it idle on concrete. It should quickly heat up and let you find any external leaks ( thumpers will overheat without air passing over radiator. If it's not boiling out ( like out the overflow because of week cap ) or somewhere else, the next logical place is in the engine or tranny oil. If that looks good, it's probably the head. The blow by on the breather would lead me to suspect cylinder pressure is leaking into the case.