The 490R and 490T pickups are the modern equivalents to the '57 Classic pickups. The 490s have a 4-wire connector cable with which different switching variants are possible (coil-split, serial, parallel).
The 490R and 490T have different spacings between the pins to provide better balance to the increasing string spacing towards the bridge. Both pickups feature vintage Alnico magnets. The 490R is installed in most Gibson guitars as the neck pickup, and is often combined with the 490T or 498T.