This day in 1971...

[lazy poker]

. . . thanks a million, aleuzzi!

But you're not quite right in terms the city - the "Coming Home" documentary (thanks for pointing this out!) shows the pic zooming in from under the marquee of the "Fillmore East" in New York, so that's clearly the location.

And taking in account the Mac having been on the same bill as Fairport and Savoy Brown, I'm pretty sure that the 3 gentlemen in question outside of the Mac are probably Rod Price, Tony Stevens and Roger Earl (left to right) from Savoy (definitely nobody from Fairport). So all questions answered, I guess.