Have I ruined my engine?

I used to purchase a lot of junkyard engines when I was a kid. They would always be full of rust when I go them,I would flush them and run them. So, what I would do, was install a screen over the upper radiator hose so it would catch the rust exiting the engine before it entered the radiator, then mixed a little muratic acid and filled the enigne with about 10 - 20 percent muratic, into the water, ran the engine, flushed the engine several times, each time cleaning the catch screen and mixing in muratic acid into the water. My run / flush procedure was to fill the cooling system with the solution (no thermostat) run it at varying rpms for 15 minutes, completely drain the cooling system then re-fill and repeat. After 3 flushes cycles, I would then soak the final flush cycle for 15 minutes, then take off the upper radiator hose and point it in a safe direction, stick the garden hose full blast in the upper radiator port so the radiator sucked in clean water, rev the engine to about 1500 rpm, this would blast water out the open upper radiator hose, totally shooting all left over junk out. This process worked very well on many engines. After flushing several times with water at the end of the procedure, I just ran the car with proper coolant mix, occasionally checking my screen trap. This would easily cure any overheating issues from clogged radiator or block coolant passages. Some would say the muratic acid may dissolve a head gasket or a freeze plug. I did it many times in engines with 100 - 200 k on them and not one issue. Most of the engines were from the 70s. I did have a 64 260 ci ford with rusted freeze plugs, which had to be replaced prior to the procedure.