Agreed, especially after the late '60s, though I was referring to your post measuring the 902 as 7/8" to match up to the small Mantaray. The 909 is 1" as shown on its data sheet, though in later years the 902 is listed as 1" also, but no clue if it's a typo or there's a later version 902 with a 1" to confuse us. Maybe Bill can set us straight.
Well, it's been more like falling off a cliff for me, so have to Google myself to find out a lot of what I once knew now that so much of it is locked up in a damaged HD and its backup.
Anyway, you're right about any mis-match between the horn/driver being a no-no [doesn't matter which way, sound is AC, so a double 'hit'] since it causes reflections that makes a mess of the HF response and why I ultimately wound up align honing a pair [among other things], replacing the cardboard gasket with an alum. one with wax paper gaskets to ensure a tight seal [normally another no-no].
GM

