I believe one configuration would be an R7 or R8 version using a 5 slot cabinet equipped with an ACS509, (1) EC308, and (1) 012E will give you a "usable" maximum of 48 stations and 8 CO lines. Because of the Partner architecture any stations above the 48 will be UN-usable, whether they are system phones or SLS.
Hope that helps!
....JIM....