Thanks for the comments guys and Sean for scanning and posting the photo. Like James, I checked out the Old Golf Images website but the photo was tiny but the caption mentioned Mackenzie was in the photo. This was the reason why I thought it was of the ISGCA meeting. But I don't think it is.
My thoughts on the photo:
Certainly it is Colt in the middle and John Morrison on his immediate left. I'm not convinced that is Alison at the side of Morrison in what has been described as a floppy hat. Photographs of Alison are few and far between but the ones I've seen of him show him to be tall and lanky. I've scanned the ones I've been able to find and posted these for comparison and I'll be interested in what others think.
As for the rest, its not really clear just who these people are to me. Certainly no immediately recognisable faces like Tom Simpson and definitely no Mackenzie. No Campbell, no Hutchinson that I can see. I don't think it is a group of architects, perhaps Colt with his construction team?
Anyway, below are my assembled Alison photos, the first 4 are from the Oxford and Cambridge GS tour of the US in 1903:
And finally a cropped image of the man supposedly Alison from the group photo. Does not look at all like him, carries his head quite differently and he is fairly short, shorter than Colt although standing on the same step.