Chevrolet uses either a 153-tooth or 168-tooth starter depending on which flywheel or flexplate is used on your year, make and model Chevy. Generally, the 153-tooth flexplate was used on small-block Chevrolets while the big-block Chevys used the 168-tooth flexplate, though both are interchangeable. If you have a flywheel that has bad teeth or you want to change the type of starter, simply remove the ring gear and press the new one on the flywheel. You can then change starters.
Jack up the vehicle and support it with jack stands. Look at the starter. If the bolt pattern is straight across, you have a 153-tooth starter. If the bolt pattern is staggered, you have a 168-tooth starter.
Remove the negative battery cable and the starter wiring, using the appropriate wrenches. Screw the nuts back onto the studs so you don't lose them.
Remove the starter bolts. Be prepared to support the starter because it is heavy. If the bolts are the same length, you most likely have a 168-tooth starter. If one is shorter than the other, you most likely have a 153-tooth starter.
