1991 Dakota 318 TBI Belt Tensioner made of Unobtainium

went to an aap i used to work at bout 25 min from me. i had chad look tensioner up and his l/u says dayco 89315. i looked up at home under belt tensioner assembly for 91 dak sport 318 and it still shows 89434/910556a. i asked chad why is there more choices at home than in store. he said may be that there are more sources to pull parts from than at individuals area stores.