Offshoreonly.com - 454 Mag. Only running on 5 Cyl.

1st off, It's a 454 mag. Carb. 412 hours, all stock and origanal, stock merc, exh. manafolds with a bravo. drive. Single gas tank feeding 2 motors.
I was out boating and it ran fine all day, I then went and docked it for about 3 hours, came back that night and started it to go home, the starboard engine started right up but sounded a little rough but since they are carb motors I didn't think anything about it at the time because they usally clear up as soon as you rev them up a little, I didn't want to rev it up in the marina because it was late and didn't want to piss off the rag boaters. Anyway, started the port motor and everything sounded fine, idled out of the no wake zone and once they were up to 150 deg. I eased it up on plane, it was dark so I was only running about 2800-3000 rpms when all of a sudden we heard a ticking sound like a lifter makes, my buddy went to the back as I was lifting the hatch, as the hatch opened it sounded more like a knock. It would idle rough but no knock, as soon as you start putting a load on it, it knocks. I shut it down and came home on one.
I started working on it today. It starts right up but is rough, I thought it was just missing on 1 cyl. so a started removing spark plug wires to pinpoint which cyl. #3 #5 and#7 didn't make any difference in the sound, so I then removed 3 5 7 all at once and it didn't change, thouse 3 are all on the port side along with #1, but removing #1 by itself makes a big difference. There is no tick, knock or hammer when it isn't under a load.
I also noticed what looks like small drops of water when a shook the PCV tube coming from the port side, the starboad side tube looks a little milky.
What should I look at next? Valve springs? valves? Does this sound like a reversion problem? Or electrical? Thanks, JB