I looked up the part number you listed in Galens white books,and those books show no 273 with a 727 behind it in 66. Now in 65 a 273 had a 727 but that was police/taxi in the B-bodies. Look at the pan by the dip stick tube and see if it has an outward hump there-if so its a 727 and if its just straight there its a 904. Galens book lists it as a 66 A body 273-2bbl. Are you sure the last number is 8? as a2538333 is a 66 318 727 trans.