His tone did change a lot over the years. You'd never guess 90s, 80s and 70s Iommi is the same player. He went from stock pickups to P90s. to very high output mini humbuckers, to really high output regular-sized humbuckers.
The twin-blade version of the El Diablo IS the original Duncan "Iommi" pickup and what he used in his Patrick Eggle guitars during the '90s: http://customshop.seymourduncan.com/el-diablo/
I have a Duncan A2P set in my SG. Love it, but i never tried to aim for a pure Black Sabbath tone.
If i had to be go for an early Sabbath tone, i would look into these : SD Phat Cat / Bare Knuckle Manhattan or Blue Note / The Creamery Hum-90 or Sonic-Six / Gibson P94.
I think the duncan sh6 distortion is a good candidate. if you get a 4 conductor version, you can experiment with out of phase or coil split. You can probably snag a used one at a decent price.