First, don't worry about the missing J in the sticker, they never have the suffixes. In most cases (not this, though), they're just a finish code, they would have needed hundreds of stickers to cover all the variation, so I guess they settled for just the model numbers.
The three J-models (500, 600 and 800) have different switching, the 500J have the least complex system, just on/off/phase per pickup. The 1980 catalog describes it as "Brian May-like", the Red Special has the same setup, though with six sliders. It's relatively straightforward, you get all the standard sounds plus bridge+neck and all three, plus whatever (usually fairly useless) out-of-phase tones can be found between them. It adds up to 13 settings in all, according to the catalogs.
I've had a 600J, that was quite different, involving one two-position switch and two three-position. There was a lot of series-parallel trickery going on that I honestly can't remember, but one possible tone you could get was the bridge and middle together as a humbucker. But as I recall, some standard settings were lost in the process. I do believe that the 1979 SE800J was the same, but in 1980, it got the Schecter-style SE-1T tappable pickups, and I can't even begin so speculate what kind of switching weirdness they dreamt up for that one.
They're all a bit like combination locks in terms of user-friendlness, but I should think the SE500J is the most intuitive of them, for what it's worth. Should be an excellent to amazing basic guitar though, and the pickups (Maxon PU-100W) are very nice indeed.
