Between the fact that it's a t-shirt transfer (probably has release paper over the image) and the scan resolution, it's not really a Photoshop job - you can boost the color and sharpen it a bit, but the detail just isn't there to repair - you have to recreate it. I'm endeavoring to trace it in Adobe Illustrator and make actual vector art out of it, but it'll take a little time. Having said that, the processes used back in the '70s were considerably less sharp and precise than the way we do things now, so the art will definitely have a slightly different look to it - stay tuned.
That is a very cool image!
I was going to try it but have at it! I think you can change the vectored lines in Illustrator to slightly grainy ones, or you can export the Illustrator file into Photoshop and adjust it there.
I'm working on recreating the '60s bird now and realized it's not nearly as clean up close was when you casually look at it. When I finish the '60s I'm going to do the '76 p/g, then the '79 Bird.