I think the GN rims would stick out too far. GN off set is in the middle of the rim, the late '80s FWD Century's off set is toward the outside of the rim. Hope this makes sense.
get the old Riv wheels - they look like GN wheels w/ the offset(according to the most recent Hemmings Muscle Car, the riv's had the wheels 1st and then GM jsut ajusted backspacing for the GNs)