88 was the first year (you probably already know) and the serial was indeed on the back of the headstock. There should be a "PRS Electric" on the front of the headstock. Yours was the 341st one made. Mine was the 487th. It's an Alder body. Don't sell it. There aren't many of them. I'd put the original tuners back on.
Also check the pups to see if they are original. Should look like this: