I'm not aware of Alnico 1. I don't know if it even exists. Alnico 2-8 have been used in pickups though. Apparently some of the PAF's used alnico 3 and 4. Lindy Fralin's humbuckers use a4 and so do many of Bare Knuckle pickups. I'd bet that there are other boutique pickups that use a4 too. The original p90's used a2 or a3. Lipstick pickups (as in Danelectro) used a6. I think some of the Ibanez pickups used a8 (edit -- true it was the Super 70).