First off, really cool item! If you come across the COA, I saw some stuff online going for the $3-4,000 range with these two, so if it is real and there is paperwork, congrats to you!
Here is a site with Ali's signatures over the years:
http://www.aliautos.net/examples.html. My initial thought was that both look real, and Ali is a tough one, since as his condition worsened, his signature got a lot more shaky. There is a short article on the site about Ali during the 70s, saying that he was on the go everywhere, and his signature varied a lot. He has a reputation as being a great autograph signer during his life, though lately I think his health prohibits him almost altogether.
Any signature is going to vary based on location of the signer (i.e. standing, sitting, walking), circumstances (i.e. sitting waiting for a plane vs. getting into or out of a car, etc.). Two more points in your favor: the owner of the magazine is from Chicago, where LOTS of celebrities visit for conventions, sporting events, political events, etc. so the chances of Ali and Frazier having been there (probably at different times and different years, realistically, as it is clearly not signed with the same pen) is very high. The other factor in your favor is that this is a SI magazine, not a canvas or another very high dollar photo or item that is more likely to be forged and re-sold for major $$$ (not that this wouldnt be worth a lot, there are boxing collectors who would drool over this!!).
I really see a lot of similarities in these signatures to ones online I see that are authenticated, so I think you do have the genuine article there, but cant say for sure, since I wasnt there when this was signed!
God Bless,
Kevin Mc
