There's this page. If that is the same guitar, it looks like a black Gibson J-200, similar to the Everley Brothers model they put out. Hard to see any detail on the headstock, but it could also be a Guild I suppose. But my money is on it being a Gibson. And, yes, the good Gibson guitars always had a unique sound especially preferred by the singer/songwriter types of Simon's day.

Paul Simon also often played a Martin (especially with Garfunkel), not one of the big dreadnoughts, but a smaller deep-waisted OM style.