Expert, I am not! But a few pointers I've learned while waiting for the same thing to pop up on CL
A 26 is a fairly rare bird since they're (typically) not sold locally off the shelf. When sellers refer to their grill as the "large" one, they pretty much mean the 22 in comparison to the 18 or the Joe. I went once to grab a 26 (no photo) where the seller assured me it was the 26 only to find out it was the 22.
The newer ones are all OTG and no 'silvers' in the bunch. I'll ask the seller if it has a pie pan or a bucket under the bottom kettle and that usually eliminates half of them. The 26 has 8" wheels compared to 6" wheels of the others. The triangle has more bars. The lid handle has a heat shield.
That's what I look for during my searches.
Here's a 26 next to a 22
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A 22
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A 26
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Note the wheel change Craig referred to.
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The older flat top Craig referred to.
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