1994 DT85 still overheating

[Danno64]

2 years ago my overheat alarm went off. Always run in salt. Pumping water well through pee hole. Brought it in and the authorized Suzuki repair shop replaced impeller and thermostat. Next time out it overheated again. I pulled the water jacket off the head and found it to be encrusted in krud. Cleaned it out and took it out again. Overheated again. Pulled the thermostat and worked good. Needed work last fall (thought the carbs needed rebuilding, but found water in gas). Technician advised me that the plugs fouled due to lack of thermostat. Over the next 3 months used salt away to flush motor. Put the thermostst back in and took out Sunday. Overheated again and now making noise in the head. Found a thread on this site indicating there are water lines around the head? If so, thinking they are likely plugged as well. Compression check 145, 140, 145. Did I blow my motor? What could the noisy head be? I am mechanicly inclined, but have never rebuilt a motor. Do I attempt, or do I have a really nice anchor on my hands?
Thanks in advance.