Ibanez blazer 81' third pickup?

Hi. i'm thinking of selling an I banez blazer that i've owned for many years and have been doing a bit of research to get a roundabout figure for sale, but I can't seem to find one the same.

It is your usual Blazer ash slab body/maple neck with the two p-bass style pickups, but it also has a jazz style pick-up at the bridge. Any ideas? is this stock or not? It certainly looks it. I'll try and get some pics up.

Cheers guys