There were 75 B-57A/RB-57As built, virtually to the British pattern save for trading the Avons for J65 (Sapphire 100).
After that came the 200+ B-57Bs... these had a new "fighter-cockpit (fore-aft seating), a rotating bomb bay, fuselage-mounted speed brakes, 4x.50 Browning mg in each wing (8 total), 4 stores pylons under each wing (8 total), as well as more minor changes.