3.91 good or bad

it will cost you more than 400$ to buy gears bearings and set up the rear end. I like to keep a variety of rear ends for different moods. you can sell and buy for even money if that's what you want to do. They aren't that hard to swap out for a variety.You can buy one complete for the cost of changing that one over. then you'd have two. I have a rebuilt 742 3.23 clutch stile id trade even but then you wouldn't have 3.91s any more.