I've been hitting Gettysburg that weekend for the last 10 years or so, & I've never had a problem with those spots late Friday, early Saturday, or early Sunday.
I believe most people don't know you can walk the charge route, it's never been crowded when I've been there.
Watch out for the Boy Scout troops - I've never heard such goshawful language in a public place, the adults with them don't seem fazed at all!
If you see any Segway tours, & you're driving, pretend they're duckpins!
Where I see the biggest crowds are the ghost tours - what a racket!