From the website:
The pickup family includes the Fender-ish bright 63, the more agressive sound of the 66 and the 66S (optimized for single pickup application). I also offer a 5 string modification that "stretches" the magnetic field across the wider span of the 5 string, but fits in the same can.
The 63 Series: 63 Neck and 63 Bridge. Replicated from early Gibson samples, these pickups are bright and growly, somewhat Fender-ish in tone. Customers report these shine for recording applications. The bridge pickup is more powerful than the neck pickup to get good balance. Specify pair or single neck or bridge pickup when ordering.
The 66 Series: 66 Neck and 66 Bridge. Replicated from later Gibson samples. These pickups have a nice balance between power and brightness, and have been our consistent best seller. Again, the bridge pickup is more powerful than the neck to maintain a sonic balance. Specify pair or single neck or bridge pickup when ordering.
The 66S Pickup: Optimized for single pickup applications. It has somewhat more power than a 66 Bridge, but maintains a good amount of brightness. I call it “pleasingly plump yet crunchy”.
Our pickups, fully assembled, are 3.65" x 1.59". Vintage Gibsons are approximately 3.63" x 1.56", so measure fit carefully for your application - there may be an interference in the width of the body rout