I wondered about the P90's in my Historic 54 LP also, because they sound so good. Looked into it a little and found out there is no special wind. Just the stock Gibby P90. which just happens to be a nice sounding pickup.
So your Custom Shop Gibby uses their stock pickup.
I have/have had more than my fair share of Gibson P90s! Always love them in the bridge, on some guitars the neck pickup tends to be muddy even with playing around with the height, but on others it's beautiful.