Hey man,
I run a similarly cheap M500 as my "walking around the property" gun. My other long guns cost at least 3x as much, but it's the one I pick up the most. Go figure.
I would highly recommend replacing your magazine spring. I'm not sure if they were using loc-tite on the magazine tubes during that era, but to be safe, heat her up real good with a hair dryer and twist the mag tube out. While you're in there, you might want to spend the extra $10 or so on a polymer mag follower.
Screw it all back together, mount your XS bead and your flashlight. Done. You're ready for damn near anything.
If you want to be super high speed low drag, you could velcro a shotshell card on the side of the receiver.