WES-T is an open diff 2-pinion 28 spline 9". The yoke on yours is a "tall" 1310 series yoke, used in pretty much all 71-73 351 powered Mustangs except for the highest performance cars.
Alan Van Aunen owns and runs 8and9inchfordrears. The guy knows his stuff, and will be getting my next diff order. He builds the rears personally, not some guy who works for a company.
8 and 9 Inch Ford Rears Custom Built for Street to Race Applications. From stock Trac Loc posi to full-spool, all-out race third members.
8and9inchfordrears.com
He also has an eBay store so you can see what the pricing and options are. He quoted me prices below that on the eBay listings a couple months ago.
www.ebay.com