The 4 speed overdrive was the MY6, and was a GM bolt pattern version of the Chrysler A833 4 speed. The GM version isn't very common.
You may want to consider a different tire size. The 225/60/15 is only about 26" tall, much shorter than the oem tire. While it would be ok for acceleration, that diameter tire will kill the speed unless you gear it real high. A 225/70/15 would be better.
