I played a '71 vintage Guild M-85 II a few months ago in an NYC vintage guitar shop. This one, in fact:
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According to Invalid Link Removed, the bass I posted has the stock pickups.
The pickups in your bass? The neck looks like one that's commonly found in a Guild Starfire (or it's a Darkstar). That, plus the odd bridge pickup make me think that your bass is an M-85 I, which came with a single pickup in the neck position, much like the Starfire bass's pickup. The bridge pickup was probably a mod made by the original owner who wanted a little more tonal versatility.