I wasn't aware that the original G&L *MFD Pickups had slotted polepieces.
(like this) In 1983 i bought a
G&L El Toro bass with *MFDs, and each string has four polepieces on each pickup. Those -
and every G&L I've ever seen, until now - have hexagonal slots, so you can adjust them with an Allen wrench.
At the time I was torn between a five-string Music Man bass (also designed by Leo Fender, y'know) with active pickups or the El Toro. Mine's passive, though they offered actives as a custom option.
Leo had been prohibited from launching a new guitar company for 15 years by the non-compete clause in the sale of Fender to CBS in 1965, so when he and George Fullerton (the "G" in "G&L") started their new company in 1980, I was convinced they'd quickly overtake everybody else, and the El Toro - G&L's first bass with humbucker *MFDs - would be worth a fortune, so I bought it. Turned out they only produced them for a very brief time, because nobody but idiots bought them.
* I can't figure out what the "D" stands for, but I can guess the rest.