randy's ring & pinion.com rocks for low priced gear sets. I bought a 4.10 set and a rebuild kit for my 99 Lightning's 9.75" rear. It was Yukon brand and I felt the price rocked.
You may want to check on some Mustang forums. I believe they also have an 8.8 rear and I'm sure that the 4.10s are a dime a dozen on their swap and sell forums.
mustangs didnt come with 4.10s only few rangers 4 bangers and the fx model, i have set of 3.73s.
went to salvage thought i got lucky finally found a ranger with 4.10s got them home went to put them on wouldn't fit they were off a 7.5 so took them back and couldnt find any 4.10s so exchanged them for 3.73 they were everywhere. only paid 59 dollars for these gears so if anyone needs a set let me know 59 plus tax then i think usps has the $10 box if it fits it ships
I have the Summit racing 4:10 motorsports gears. They will fit but you will get more noise out of them. They are differant than the ford truck OEM 4:10 gear set.