interesting...No skunk stripe...The decal looks like it's aged right along with the neck,
but there is no 'guitar' after 'F-100' and no series designation.
The bottom headstock bout sure says S-500 to me ,
<---like in my avatar.
The point looks a little stubby, but it could be the angle of the pic.
I've reshaped one invader headstock that someone cut off the point, it's not easy to make it look 'right'.
This one looks pretty good ( and no light spots on the edge that might happen if the wood was cut after leaving the G&L) so I'd hazard a guess it is factory.
My guess is that someone got a replacement neck from G&L and they used a S-500 neck
(I'm guessing 82-86) . The tuners say 85-86 to me...but I'm no expert, I'll have to bone up on the
G&L factory tuner timeline.