I have an original Sheridan (pump) that's older than that. I had the Sheridan factory rebuild it for me in 1970 or 1971 (I obtained it used). It is an awesome little air rifle. I am more fond of it than my fancier spring guns. As you mention, too bad yours is not a pump.
Google it and you should find a fellow that specializes in these - I don't have the site on this computer. Plenty of info available on these.
The pump version, with some of that fellows modifications, is very well thought of by folks who actually use them long-term out in the boonies.