Well, technically, it was the original '70s Bill Lawrence 500XL (from which the Dimebucker was later modeled) that Mr. Duncan rewound for Eddie, with the magnet swapped for an A2 out of Eddie's broken PAF. Seymour intentionally overwound the 500XL to make up for the reduced output of the A2 mag, creating the wind that would eventually become the basis for the SLUG
But there's also the rumor that Eddie cut off the ends of a P-90 with a table saw in order to stuff it in a humbucker rout, which got me thinking that something like the Phat Cat, another humbucker-sized P-90, might actually get in the ballpark tone-wise, at least for the first album sound