The uncertainties of saying "uncle"

For work today, I'm interviewing Corporate Overlord's dad. We all used to live in the same housing estate, so I would have seen him around the neighbourhood when I was growing up and he would have been one of the many "uncles" that I said hi to.

On the other hand, I haven't seen him in almost twenty years (really, I have no clear recollection of what he looks like) and when I arranged the appointment with him over the phone earlier this week, he referred to himself by his first name.

So the question is: what do I call him when I see him later?

• The handy, friendly, all-purpose "uncle", since it was through his son that I got in touch with him?
  
• By his first name since he thusly identified himself when he called me?
  
• As "Mr _____", using his last name? But then even the "Mr" gets dicey since he, like everyone in that neighbourhood back then (more about that in a subsequent post), was a military officer.

My boss is going to be at the interview too, so I suppose I could address him by whatever he introduces himself to the boss as. And I am meeting him in a professional capacity ---

--- Although it's a personal favour that got us the meeting in the first place. Above all, would it be weird to not call him "uncle"?

Argh!

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