make sure the head is off
Hit the cylinder with a hammer
Don't break a fin, BUT hit it hard on the sides so you contact multiple fins in a rocking motion
buy a kit
to check ring endgap you can just throw a ring in the cylinder and measure it like that with feeler gauges
As for cleaning a head; I just scrape the inside of the fins with a screwdriver. On the outside of the head, I hit it with a brass 6" wire wheel on a bench grinder. The brass doesn't scratch the gasket mating surfaces, it only cleans them up so you dont have to be gentle, just dont really go into the cylinder I guess.
Otherwise the other option would be sandblasting I guess. I would like to clean mine up better but I wanted to make sure it was clear for airflow too.