Is it worth it on the gs500? I already have my head off just wondered if it's something worth doing on the gs.
Unless you're combining it with other mods like bigger pistons, cams and flat slide carbs, no.
a real port and polish is hard to do. you'll need airflow test equipment and an army of files, scrappers, and sandpaper.
i would suggest you just clean up the casting marks (if any), and knock down any high spots if you see any. don't make any drastic changes tho.
And it might be worth it to run a dremel in the exhaust pipes, grind the weld down to pipe ID.