I think it is possible they are the same man, but still wondering whether the moustache is clouding my judgement

We know that Archibald and Dulcie were at Balhomie between 9th-14th October 1907 from "Grandmothers photo album". Archie would have been 40 years old and Dulcie 34. I think the unknown man does look about 40 in the photo.
Archibald and Dulcie had only been married 6 months when they signed the photo album. They married at St. George Hanover Square, London on 9th April 1907. I wonder if the wedding was reported in the newspapers, it may also list guest names.