Jerry mostly used the middle position set in the single coil position. It's definitely one of the many factors it that tone but not the only one. If your guitar is already routed for humbuckers you might as well get a humbucker. While your at it I'd get a coil tap switch. It's not that big of a job and most good pickups have the wiring to tap them. Whether or not you're going for a Jerry tone it gives you more tonal options. I'm assuming you have a 2 pickup guitar. Jerry used the middle pickup mostly, there's something to the placement of the pickup that goes into that sound, you can get close with a 2 pickup guitar. Jerry used several of them early on. He used P90s on at least one of them.
I'd rate the order of importance of his tone as:
2. Amp (Twin preamp, Mac solid state power amp)
3. Guitar type - neck scale, high action, wood choice, string gauge
4. Electronics - pickups, electronics, coil tapped middle position
5. Peripherals - string brand, picks, etc.