I was at one of the local pick and pull junk yards yesterday. They had a 88 Turbo Coupe with an automatic. I thought these were supposed to be 3:73 gear ratio. For $100 I could pop the whole assembly in my 92 and get the 3:73s I wanted. I pulled the rear cover off to verify condition and to make sure it had the 3:73 ratio. It turned out it had 4:10s. More than I want, oh well. Did the Turbo Coupes ever come with 4:10s? Or did someone put them in? If anyone in the SLC area wants a diff with 4:10s let me know and I'll tell you where its at.
I guess I could have been like you and bought it, then bought some 3:73s and put them in the differential. Or I could save the $100 and buy some 3:73s for the 8.8 already in my car. Its still there, for a fee I'll pull it and send it to you. You can pay shipping.
I looked at the 4:10 diff, Flava got the diff with 3:73's and 4 lug axles.