The Mule is based on the early PAF humbuckers circa '58, they're wound with offset coils of 42 gauge plain enamel and feature Alnico IV magnets, unpolished and cut to the longer vintage length. The output of the earlier PAFs varied with DC res anywhere form 8 to 9K. I've based the wind on the best sounding I've heard and also what I considered sounded best to my ears.
These are my favourite humbuckers, they're full and punchy without being dark or suffering mid spikes, the highs are clear without being brittle and the bass is warm without being flabby or, at the other extreme, surgical.
I've spent along time working on the wind of these, especially the often neglected neck trying to achieve the optimum balance of power and tone.
Stormy Monday humbuckers are based on the later patent number pickups with a lower output. The materials and construction are the same and, unlike the patent number humbuckers that employed Alnico V's, I've stuck with Alnico IVs simply because they sound so much better in this application.
The tone is more open than the Mules, brighter but less power. They make a great neck pickup in combination with some of our higher gain models and a great bridge for semi's or light solid body guitars. My preference is for the Mule although Stormy Mondays have found a place in several of my LPs particularly Standards and Deluxes.
Both are available in calibrated sets and this is the best way to buy them-they're sold as a pair and wound as a pair, properly for each position.
Hope this helps-call me anytime if you want to talk more. :D