I think Rocky Rotella discusses WS7 in his book "The Definitive Firebird & Trans Am Guide: 1970 1/2 - 1981".
John M Witzke in his article '1977-79 T/A 6.6 HISTORICAL INFORMATION' stated
"..additionally, in mid-December 1978, Pontiac released a new suspension package called “Special Handling Package” and carried UPC code WS7. This suspension package was identical to the WS6 minus UPC code J56 front and rear disc brakes. The WS7 handling package was not available with code UPC L78, T/A 6.6 engine or the Y84 black and gold special edition Trans Am. It appears the WS7 was available on both the 1979 Firebird Formula and Trans Am. The cost for the WS7 Package was $284.00. The 1979 WS7 production accounted for 11.2% of the total Trans Am and Formula production or approximately 15,899 cars..."
See
http://pontiacformula.free.fr/schema/W72.pdf