Rear drum brakes

And when you put that 2.5" drum onto the studs, and push it on, the rim of the drum will hit the 2.0 backing plate showing a large gap between the back of the drum-face and the axle flange. If you look for it, I think you can see it. If not, you can tell it's wrong because the hub-centering ring on the axle, is not protruding thru the hole in the drum correctly.
There is no cure for this other than to use matching parts.

But here's the wildcard;
If the shoes are too wide, the backside of the drum faces might hit the edges of the shoes first,lol, even if the drums and backing plates ARE matching.. That is why the shoe width is about .5 less than the drum depth.