Are John Mayer's pickups just Fender Fat 60s? Are they just "tweaked" Texas Specials?

I heard that John Mayer's Big Dipper pickups were re-branded as "Fat 60s" when he left Fender.
To investigate this claim, I reached out to the Stratocaster community to get some information about these pickups.
If the rumor is true, how different are Fat 60s from stock Texas Special pickups? After all, John's Big Dippers were based on an underwound set of Texas Specials...
Stay tuned to hear a comparison between some pickups and find out where my research led me!