The pics really make it hard to judge but I would say you did OK.
The screw behind the hammer is either loose, the wrong screw or it had a peep sight on it at one time.
The third pic color of the right side of the receiver just ahead of the loading gate shows maybe some blotchy spots which may or may not be the result of an old reblue.
Hard to say for sure from the pic.
Most 73s came standard with a buckhorn style rear sight.
The last pic shows more of a modern style more typically found on a model 94.
Again, hard to say.
Could have been replaced.
Over all condition IMO would be a little higher than 50%.
The old 73s saw heavy use and this one looks a little nicer than what you would usually run across in the price range you got it for.
The round barrel was standard but really is more rare than the optional octagon barrel.
Most people seemed to want the octagon style back then.
I would say you got a pretty good deal!
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LONGTOM