Great question — answering as the UphillTech team:
It's a question of clearance with the chainstays. There are many mountain bikes that won't have anywhere near the chainring clearance you need for any one of those rings in their respective positions. The 50 is the likely culprit. If you're talking old enough, i.e. back in the days of extremely long chainstays, that can be different. Even if the all the rings clear, the next problem is crank clearance. It's not a hard no and if it's steel, in some cases you can dimple your way out of it if you're willing to modify the frame.
Full answer by Nathan Knutson: https://bicycles.stackexchange.com/a/95842 (CC BY-SA 4.0).
Need it done for your business? UphillTech.
