I'm pretty sure 98 should be "Ninety-Eight". I'm not so sure about 88 though...

Here it says "88":

http://upload.wikimedia.org/wikipedia/commons/d/db/77-85_Oldsmobile_Delta_88_Coupe_1.jpg

Here it says "Eighty-Eight":

http://www.imcdb.org/vehicle_80122-Oldsmobile-Eighty-Eight.html