The 960 was made from just after WW2 to about the mid 1970's,,maybe 1976/77.
They made a 961 model,,same revolver but in nickel finish. Those were mfg'd late in production I think.
Should be ser#'d bottom of the butt frame. H&R used a letter prefix with the ser#. The prefix was a yr/date code.
Here's a good reference to the codes and yrs of mfg they represent:
Harrington & Richardson date codes
The revolvers are a simple pull the center pin, drop out cylinder and use the center pin to poke out the emptys operation.
I recently had a customer bring me one that he had put conversion inserts into the 32cal chambers to enable it to fire much cheaper #209 shotshell primers.
I put lighter weight springs in the action, put a lanyard ring on it and made an oversize set of checkered walnut grips for it too. His wife uses the revolver in K9 field trial work.
The tiny factory grips and orig heavy DA pull didn't work out too well but now with the mods it's a favorite I understand.
I'd guess they sell for around $100 +/- in nice condition,,just a guess though on my part. I didn't ask him what he paid for his.
Check the gun auction sites,,closed auctions,,should give you a good idea what the market is on them.
They made a .22rf blank caliber edition too. Model 970 (blue),,971 (Nickel)