Welcome to the Forum OP! I believe you got a nice deal on a nice gun. Some items I've noticed and been educated about by the experts on this forum over the years that may be of interest to you about your K22 Masterpiece.
Last year I sold a 3 digit, K22, blue (K 905) that shipped in August of 1947. This date was confirmed by a Factory Letter of Authentication. It had what is known as a "one line address" on the right side of the frame.
Also last year I sold my other K22 Masterpiece, blue finish, serial number K 42372. This may be the gun that Jack (JP@AK) is referring to in his post above as it is a little higher than yours and mine was confirmed by S&W Historian as shipping in August 1948.
The 1948 gun pics below show that it had a 4 line address, high speed (aka short) action, large S&W logo on right side of frame.
These same features should be present on your gun if unaltered from original. I see one poster above spoke about yours's having a 1 line address but I cannot see that from the photos.
If you could post some more pics it would be great as we LOVE photos on this Forum!
I think you did just fine at $700. When I sold the 2 I had last year, they both went to the same collector and price realized (after shipping costs, transfer fees, etc.) was a tad less than $1,000 each.