This would be the correct David Mitson. He was a local artist of good reputation who lived on York Road in Dundas, Ontario (Wentworth County). He was also bandmaster of Dundas Concert Band (succeeded in early 60's by my father Charles Evans after Mitson's retirement). He did in fact design the windows of the Mohawk chapel around the dates you have stated (believe Chief at time ws named (Edward ?) Burnham. David Mitson was also bandmaster of the Six Nations band at same time. Several members of Dundas Concert Band (including my father) were also mebers of the Indian band at that time. I believe the windows designed by Dave Mitson have since been replaced because the church has been renovated, probably more than once, by then. I remember Dave Mitson as a caring, personable gentleman who was often seen walking his gorgeous English setter (believe named Daisy) along York Road in Dundas in mid-late 50's. I can't remember his wife's name but she too was a lovely, delightful lady. My older sister tells me that David Mitson was the Indian Agent for the government but I am not sure if this is correct.