Well as far as I know there were three XLT Lariat rapid spec packages. The 507 was the most comprehensive one. The 505A had the nice interior but didnt have the power equipment, the 506A had the power equip but without a couple things, and the 507 had everything.
http://storm.oldcarmanualproject.com/ford/pickup/1988/1415.jpg
http://storm.oldcarmanualproject.com/ford/pickup/1988/1415.jpg