Mike wrote this to me a while back and I think he is 100% correct:
The discussion last week about Marty’s U.S. Patent Office shirt got me thinking: I could be wrong, but I think this wacky description of our hero refers to Eric Stoltz’s wardrobe from his brief tenure as Marty in the first BTTF. Most pictures have always been hard to see, as he’s wearing a jacket, but I have a feeling the guitar diagram on his shirt in pictures like [the bottom two at the top of this post] is supposed to be set up like a diagram you’d see in patent paperwork. Unfortunately, there’s never been a great color picture of Stolz’s wardrobe to indicate if his shoes are green, which would solve the puzzle entirely.
And for those of you who didn’t see the movie, YEP: they filmed 5 weeks of it with Eric Stoltz as Marty before deciding they weren’t getting the laughs they wanted, fired him, and replaced him with Michael J Fox. Here’s some of the Stoltz footage!
What’s interesting about all this is that the filmmakers obviously did some “let’s make this movie better” rewriting once Stoltz was gone (at least some wardrobe changes which necessitated new lines) and from other stuff I’ve read, this is probably the point at which they dropped the “everybody dies” beginning. It also means that if Gipe was imagining an actor in Marty’s role while he was writing, it was a different one for at least some of it. Maybe that’s why Marty is such a future dick all of the time? Doesn’t explain Doc, Gipe’s weird asides, or any of the other characters though.