Most keycaps have different height caps on each row too, making this a big and complicated list...
ISO left shift is 1.25 wide vs the 2.25 ANSI version - if you want the correct legend you'll need an ISO kit.
The bottom row mods are all 1.25 in a standard set to go with a 6.25 spacebar, another common bottom row that's included in the base kit of most custom sets is 1.5-1-1.5-7-1.5-1-1.5 which mimics the old winkeyless layout - look out for the big spacebar to know.
The other common non-standard mod is the 1.75 split right shift and an FN key to go next to it. This is usually in the base set too in recent sets as 60% boards are so popular.
Anything else you're looking at extra kits which may not be available in every set, so if you plan to swap you may want to avoid them.
You are looking to design a custom board, right? If not I probably failed to answer
