Call me weird but I've actually just installed a Gibson Tony Iommi in the neck position of my Gibson SG (AV Warpig bridge), replacing the stock 490R. Sonically, it's working out quite a bit better than I expected, and thematically, of course, it's just perfect! It's a tad brighter than your average neck PU, but that's alright, because SG neck pickups tend to sound mushy otherwise. It sustains beautifully, and its tone seems warmer and fuller in the neck position than in the bridge position where it tended to sound somewhat dull and colorless. It's got a DC resistance of 17.2k and it can (just barely) keep up with the bridge 21.5k AV Warpig! :D (The Iommi isn't actually quite as hot as the DC resistance implies, probably due to the use of Alnico II along with the ceramics.)
But as I said, it's a very good match both sonically and thematically. It rounds up the "metal SG" concept pretty nicely, and all 3 positions are extremely usable, from beautiful cleans to full distortion in all positions. Aside from the obvious BKP alternatives, that is something to consider. For BKP, I would probably just get a neck version of the 'pig, or maybe something to give me an Yngwie-like lead sound (or an approximation thereof) in a humbucker-sized package - MQ, perhaps?