hi, my name is XXXXX XXXXX I will help you ..
if after all the things you replaced and the fan is working ,I would think the next thing to do is to do a block test .
this consists of a tube with a squeeze bulb on top .the tube is partially filled with a special blue colored chemical .
the motor should be a little warmed up and while its running and not overheating yet ,you place the tube over the fill hole and squeeze the bulb to draw in coolant fumes .
if the blue chemical turns a light brown/yellow or greenish color the you either have a bad head gasket and /or cracked head(s)
in either case the heads need to be removed and taken to a machine shop to be checked for cracks/warps
I would suspect cracks in the heads as this has been overheaded badly as you stated .
the block kit ,runs around $60 at most auto parts stores ,
you could get it tested at an auto repair shop and I would think that they may charge you an hours labor and the cost of the chemical although it should be a standard test and that should be an hours labor ...jazzmaster ...