I had to replace my jib sheets and the originals setup was very simple. Basically is was a single line 32 feet long folded in half. The middle was pushed through the eyelet and then each end was pulled into the loop created by the rope. You pull it tight and this creates a smooth attachment
Cow hitch is easiest... Also keep in mind Catalina liked to use 1 size fits all on most of their boat. The 3/8" line they used for jib sheets is crazy overkill (they used it on boats up to 27 feet!). Probably drop down to 3/16" or 1/4" line. Sta-set is fine if you aren't racing (try ebay). I'll offer another knot that works well, a standard bowline. I tie 1 bowline in mine (on any of my boats), with the tag end being the starboard side and the other long lead being port side. Divide the sheet in half, and tie the bowline there. Ignore how long the tag line is, it's just another alternative, the advantage of it over the cow hitch is that it is still very easy to untie.
Stay away from shackles if you can. Now I don't pay attention to my own advice, as I have a light shackle on my bowline now, but it makes headsail changes quicker.