tryin to break in new engine, ruff idle

Maybe that cylinder had bad valve guides/seals and allowed more oil to leak in and help to lessen wear on the seats ? i don't know, just guessing, maybe some other guy did the last cylinder and didn't grind as deep ?

Maybe they forgot to do that last one ? maybe you got new valves on old seats--not likely but maybe they did forget to do that one cylinder ?

You know you still can do a compression test with a cold engine. The lifters should be full of oil so I would pull all the plugs out and spin the engine over with the starter till there is some oil pressure. You can pour some motor oil over the cam and lifters so the cam doesn't wear.

Once there is oil pressure then start the compression test.

I got this feeling it was just a very lean carb and your worrying about 2 rockers needlessly. after 2 weeks of sitting I can move a few rockers an 1/8 of an inch if I really try. been thought it adjusting those rockers with the intake on.