Oops I said your frame has Takahashi lugs but then I looked at the pictures... D'oh! Those are Henry James (Folson) lugs. That's what the first Challenges were made with, before he got the Taka lugs. So definitely before my time there. I started in '84 and we had the Taka lugs by then, so my guess is '83 for yours.

I regret the mistake!