My uncle said he polished the ports of his '71 rotary valve jt-60 mx (2-stroke), and it made a noticeable difference. I know that polishing a more modern bike would make no difference at all, and I told him this, but he swears it made the bike more powerful because old bikes were made different.
During the process of polishing the ports he probably removed a bunch of casting flaws and that's what gave him the better performance. I remember a lot of cylinders from the 70's and just using a rat tail file to clean them up helped.
The noticeable difference was he had done some work so damn it had to work.
The polishing is done on the outside where it makes the most difference.
Bikes were made different in them days, you wouldn’t understand youse young folks, nowadays they are al’ made o’ plastic. In those days we had Iron. And we ate Lard. Couldn’t afford proper food in them days mind.