You went head to head with him the first time and won. What's intimidating you this time?
"I am worried that he will pull out my lack of experience as a a rebuttal for our professional disagreement"
You did not seem to worry about that the first time around and it's too late to worry about it now.
He didn't pull the lack of experience argument the first time around because it was an irrelevant argument then, and he would have looked somewhere between ridiculous and pathetic for arguing on any other grounds than technical and business grounds. He lost, but so far as I am concerned, he lost honorably. OK, he lost to someone with less experience. So what? Stuff happens and wisdom comes out of the mouth of babes. It happens to the best of us - yesterday, it was him. Today, it's me. Tomorrow, you'll get your turn.
Since when is lack of experience supposed to be a rebuttal for a professional disagreement? Who made up this rule - you? Disagreements based on technical and business grounds get resolved on technical and business grounds. Lack of experience has an impact if it hinders you from making an effective argument on technical and business grounds - that's not what happened last time. Because your argument carried the day.
Lack of experience is partially why people say things that are stupid and don't make sense and they don't even realize it. Again, that's not what happened to you last time. The stronger, sounder argument won and it just happened to be yours. Now, you're sweating all over yourself and feeling guilty :)
Do you know him as a petty minded, spiteful, vindictive individual who takes everything personally, or are you just conjuring up your own nightmares?
I have been out argued a number of times by people who were junior to me, but they hardly see me as a fool. One of my strengths is that I recognize a good point when I see one and my ego is not tied to everything I do including losing. I have lost arguments for the right reasons and I have lost them for the wrong reasons. He lost for the right reasons. So far as I am concerned, he did his best, you did your best and your firm is now better off from the fact that the argument took place.
I suggest that if you're feeling intimidated, you're getting anxiety attacks and you feel like voiding into your pants, now is a good time to do it - voiding into your pants, that is. Because on interview day, you are not wasting your time worrying about those things you can do nothing about, you are going gangbusters, you mean business and you are all business - Although I have to admit that I found that worrying is an enjoyable activity, and a fine excuse for not doing anything but worry :) You've got yourself in your corner, and that's a lot more than most people have.
And when you see him at the interview, make it a point to treat him with the respect that he deserves. Without kissing up to him, of course. He lost to you, but he is most probably a hell of a professional and you could learn a lot from him and he might be a very good one to have on your side.