Rough idle

proving a vacuum leak into the valley is easy; Just put a vacuum gauge on the dipstick, flip the PCV out of the valve cover and seal the covers, then start her up and rev it up a lil, maybe 1200rpm.Then wait a few seconds
But I really doubt that's your problem.

Do not let the pressure rise above 3 or 4 psi, cuz it will want to blow something out, maybe the cam plug in the BH!
If you don't have a vacuum/ pressure gauge, you can tape over the hole where the PCV was. If the pressure blows it off, yur good to go. If the tape gets sucked in, that's bad.