Ya the Mopar guys have a dear price to pay for a Dana 60 but it's an easy decision for a Mopar. It's proper and it is the strongest rear ever made for a car.
The serious racers at least have an option to have an S60 custom made. Basically a Dana60 but brand new. Even better in performance than a Dana60.
As for 8.5's, no new option exists.
I have to say that if I have to buy an aftermarket axle and diff setup, that it'll be a Dana 60. They are virtually the same price as a 9".They never seemed to gather the fanfare of the 9", probably because they were never readily available for swaps the way the 9" was back in the day. The issue with a 9" swap axle is that they suck if it's a factory 9". I'd rather have an 8.5 hands down over a genuine Granada, Torino or truck 9". The aftermarket 9" is definitely tougher than an 8.5...................
To each his own with this stuff. Most people get crazy with rear ends (I only get crazy with them if there are b**bs attached.) A properly setup 3 series 7.5 will handle 300 HP all day. A 28 spline spline 7.5 (7.625) with aftermarket axles is good for 400-450hp all day. A factory G 8.5 will handle 550-600hp in stock form, and a 8.5.8.6 with 30 spline axles is good to 800hp.
How many people are close to 800hp? I'll answer my question, some, but not many. Hence, the reason for a 9" or Dana 60 is generally not needed. But it is a bragging right lol.