The WS6 and W72 options were coupled early on in production but then separated. My four speed, built in November 77 doesn't have the WS6 option. I've added a the 15X8 wheels, a WS6 steering box and the rear sway bar though.
By the way, those WS6 subframe brackets won't fit past the reverse key out linkage on the four speed. They do fit on an automatic though.