With Thor I ran into that issue. I read the label on Leader pans and ordered replacements by those dimentions. When I got the Thor pans home, they would not fin on my Leader Arch, they were about 2" too long. To make them fit I had to build a new base stack collar. The Thor pans were exact, I had sold the Leader Pans, but they were obviously less than what the tags said, kind of like a modern 2x4. When 2x4's were true sized an exterior wall was studded with 2x4's and had plenty of strength, now you need a 2x6 because they are too flimsey with 2x4's.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.