Altec 291-16C: Need info please

[Elitopus1]

So if a 288G=291B (different phragm of course) what is the 291C the same as? They appear to have a bigger AlNiCo motor like the 288G, 288H, and 291B. Do they have a tangerine phase plug? Are the 291C=288H

I have a single 288G that I have been looking for a match. I know I could also use a 291B and change the diaphragm. Would these 291C be a match or are they different? I cant find a spec sheet