The Anniversary headbadge places it squarely around 1969 and the wrap-over Carlton-style stays are a Grand Prix signature feature, but the presence of the pump pegs muddles it up for me. At least I can't recall seeing a GP with TT mounted pump pegs.

Regardless, this promises to be a very cool project. I'm not really sure if I would repaint it or not - it has enough "patina" to be - let us say "unforgettable".