This is the center differential you want if you have high HP Miata dreams. This one allegedly has a rebuilt trac loc and looks very clean inside. I have extra shims for it in a parts bag, so it does seem like the guy I bought from is likely truthful there. I thought it had 3.55s, but opening it today it is a 3.27 ratio. It is indeed a 31 spline trac loc and this is the all aluminum Cobra spec center section. They are going for $225 on ebay for just the case. GRM price: $425 shipped to your door. $350 to meet anywhere within 1 hr if Dallas TX.