It sounds like you have some decent experience in being able to work with this guy so this "combination" is not really any different. They all respond to similar basics whether he is a un-handled Quarter Horse, Mustang or Clydesdale. VERY Handsome, good for you for taking him.
I picked up a very un-handled painted saddle horse a few weeks back. He has a halter on thank-goodness but it took about two weeks to be able to catch that halter. Similar situation, he is very sweet and cooperative, followed me around from a distance but did not want to be touched. It just took time. He watched the other horses being handled and groomed, got used to regular feeding times. I would sit in his pen and chat with him or let him follow me around and keep my back to him with a hand extended out for him to sniff, that sort of thing. When I did get ahold of him it was just to pet then let go again so that he got used to you come, you go. Grain and treats help to :) But the biggest help I have had in this type of horse is talking, I just chat away. Not sure why but they all seem quite interested and at ease.