Duane - I don't know what mileage you have on your SC, but a '90 is a pretty sure bet for some clutch plates to be replaced or more packed in to get back to spec. That article is great, but you have to decide whether you are up to the task, including tools. Plus the Mustang has the solid axle versus our independant - by the time you remove the rear plate & hanger to access the gears you might as well remove the pumpkin altogether and work on it on a bench. Also if you are considering lower gears, (3.55 is recommended for the auto & 3.27 for the 5 speed), you might as well take it to a shop & have the whole thing re-built including new side shaft & pinion seals. This is what I ended up doing on my '93 and the labor was lower because I delivered them just the diff. I can't exactly recall what it cost, but I bought all the parts from Summit originally, thinking I was going to do it myself. The gears are about $200, clutch pack $60 & say another $40 for all the seals & bearings. Overall say $500 incl. labor