Jean, I think you ought to look at a book called
"Oil Painting Secrets of a Master", by Linda Cateura.
www.amazon.com has it for about $17.95. It is about David A. Leffel. There is a wonderful contemporary painting of a black man and I think some explanation of the skintones. I have a copy somewhere, but as yet I haven't located it. Also check out Simmie Knox's site here on SOG. He is a wonderful black painter who paints a whole range of skintones.
www.portraitartist.com/knox
It would be well worth your while to look at Leffel's painting as it shows a beautiful range of unexpected color in the man's face. I think this would give you a great starting point.
Since you know the man, plan a little before hand. Check your lighting in various possible photo areas before you proceed. Gather a few props if necessary. Go through the photos you have beforehand to find his best angle. Get his height and look through your lens at standins to minimize his time.
Try not to shoot him from above, the lower the camera is when you shoot him the more heroic he will look. If he has a full chin you will have to compromise a bit as a too low angle will accentuate a full chinline.
Finally tell him how much he means to his community and how it would be a great honor for you to be able to do your best. This portrait will remind future generations of just what one dedicated, selfless man can accomplish.
Sincerely