The main thing you need to know is original vs easy open. If you can see the trigger guard hinge pin in the middle of the frame just above the trigger, it's easy open. If that pin is covered up by the forend, up near the barrel pin, it's an original, "hard open" frame. There were some conversions to ez open, as well. The oldest barrels have a single lug that engages in the locking mechanism in the action and newer ones have a split lug configuration. The part that pushes the lugs forward is different on the older vs newer frames so some barrels need to have the lugs changed.

The engravings are just aesthetic. The "mad cat" ( I call it the cartoon cat) is just sort of dumb looking compared to the original cougar on the rock scene. A lot of stainless frames seem to have the cartoon cat.

There's a variation called Armor Allow that requires special attention...because of the finish, those frames may or may not accept regular barrels...or maybe it's the other way around.

There are some variations in the safety and firing pin selector mechanisms and hammer castings but those will usually work fine whatever they are. Again, plenty of retrofits out there so that an older frame may have a newer hammer and/or selector and safety.