My rear end is 8 1/4...if I knew then (1997) what I know now I would have found a 8 3/4 rear end. Yeah it seems like an hour job to swap them, not much skill require, just brute force to hold the 3rd member up as you start the bolts--but then studs could make the swap easier.
I yank the whole axle out, had it clean, painted black my DTS here in Michigan...they did great work..just a little bit of noise that hasn't change all these years. Change the oil every 2-3 years, gears look nice, wear patterns good, no noticeable wear.
My top end is 120 now...I know, 140+ is the killer speed those old 440 cop cars could reach with 3.23..not sure my little guy could turn it that high rpms against the wind restriction but 130 I believe so.
I have my old gears, 3.21 and thought about paying somebody to swap them but its only a 1-3 trip a year...and Canada has crazy laws now were they take your driver license and car away for a week first time caught going 150 km/h or more (that is 92 mph) fine is $2,000 to $10,000 to top it off.
But the semi trucks now have speed limiters by law that limit top speed to 105 km/h..about 65 mph...so I'm thinking to get in front of a group of semis and just do 65 mph for 225 miles...but I have 75 miles in Michigan to travel.
It be a pain to go that slow the whole way and get the same mpg as going 85 mph with say 2.94 gears but the Falls area is much fun and I can take the Casino bus for $10 to Toronto if I miss the big city life.
But not going untill the weather is nice..we had 8 inches of snow yesterday and today was winter outside, cold and windy with snow showers all day long. It be sometime in May if I go..,if funds are good.