<html>I think you will find that the 164 tooth units went with the larger 6 bolt bellhousing. The updated 157 goes with the 5 bolt housing..some have different balance weight even with the same casting number..If your ring gear is worn, most machine shops can remove it turn it over and reinstall<br>Giving you New engagement surface<br>Sent from my Verizon 4G LTE Smartphone</html>