So I ordered up a 1.8 differential from Planet Miata for my 1.6. Problem is, the rear half of the differential case wasn't included. What are my options? Can I use my 1.6 case? Or should I moan and complain to Planet Miata for the other half?

 

that would be called the carrier, i would try bitchin first

 

i belive their prices only include the pinon housing.

 

1.6 carrier != compatible with 1.8 differential.

Try hitting eBay. I see diff carriers there from time to time.

BTW- slightly unrelated but there's a T1 Torsen up there right now. Currently $51 with two days to go:
http://cgi.ebay.com/ebaymotors/94-97...QQcmdZViewItem