It's the '61 SG style LP, probably. Whether it's a real old one (and worth a bit more than $500) or not is the question. Gibson has a "dating" service on their website, but it's not always reliable, especially for the Norlin years.
That model was never anywhere near as popular as the Les Paul Standard, so it can be hard to find information. I think they were mahogany, as a rule, which is lighter than maple/mahogany (my Deluxe is a real boat anchor), but some were made of ash, if I remember.
They actually predated the SG itself. Reportedly, Gibson was unhappy with the sales of
the LP Standard, so did the SG makeover...which sold even less.
The SG/LP was available as a Standard, with two humbuckers, a crown inlay on the peghead, bound rosewood fingerboard, and the usual four-knob LP wiring and tunamatic bridge.
There was a Junior, without the fingerboard binding and with a wrap-around bridge tailpiece, and has a decal with "Les Paul Junior" on the headstock.
The Custom had three pickups and gold trim, otherwise similar to the Standard.
These models were sold from 1961-63. Reissues were sold 87-92, but the serial number will tell you which series it came from. From 100 to 70,000s were issued in the early sixties, but I don't have any numbers for the later ones. Gibson's website should help you out there.