I always hear this theroy of SGs being neck heavy. How can 1 1/2 pounds of neck be heavier than 6 pounds of body? The problem on these style SGs (early 60s style) is the position of the strap button. This is why Iommi moves it to the top horn. SG standards with the longer heel/neck joint are very well balanced due to the strap button being about an inch and a half higher (closer to the headstock). So if neckdive is a big problem for you, move that strap button.
The Iommi pickups are something. Very unique sound. I reccomend using 500K pots on them or they sound kinda bad. You will definitely get the Sabbath sound from them, even though I bet those single coils do Sabbath pretty good too.