I've just refinished my pre-CBS Mustang...when I bought it, it had been re-painted already so it's okay...and I learned that most Poplar slabs are variegated blond and brown with distinct steaks of green and yellow. It's pretty weird wood. Your Mustang's wood looks uniform and if you think it's Mahogany, I'd bet you're right.
I could be wrong, but I'm getting the impression that there weren't too many Mahogany Mustangs, so yours may appreciate faster than a Poplar Mustang.
