While Reggie is a "collector" he also has a long term formal business buying and selling collector cars, not limited to Muscle Cars and Corvettes. He would be the best Judge regarding the added celebrity value assessment you seek as well as the underlying intrinsic value of the actual car itself.
Your friend should just call Reggie or Chip Gerst, who I believe was managing the buying and selling of Reggie's Cars at that time.
Chip's Face Book
L79s are certainly neat and very desirable cars. As far as the car itself, with no concrete dealer documentation, owner affidavits, a no issues VINed original engine and / or trans, a color change and an older restoration, I don't think its going to be a walk in the park to attain his asking price.