Oil control problems on 6, diagnostics on 8, oy bey!

[The Blue Pig]

I just gave a guy 500 bucks for a 71 2 wheel drive half ton lwb. He said the straight 6 in it runs, but oil is blowing into the air breather assembly from the pcv valve, which I guess could be a couple of things. I have not got it yet, so I am not sure. But, the main thing is my girlfriends truck. 350, edelbrock 650 manual and intake, headers and the rest of the engine is supposedly stock. I put new spark plugs in it, and set the timing back to 12 degrees initial. Ran like a raped ape for a couple days, then it starts pinging and running like complete crap. Oil still black, so I guess it aint a head gasket. Compression tests a week or two ago revealed all 8 cylinders @ 130#'s + or - 2 lbs overall. Ohmed out the plug wires, they seem to be good. It pings and rattles under acceleration, and it has lost a lot of power. I double checked the timing today, still at 12. But the way the truck lopes and slop's around, especially when you put it in gear, I think it has a dead cylinder. I put a ratchet on the crank pulley and turned it and watched the rotor, didnt have too awful much play in the timing chain. I will pull out the plugs again, and see if they tell me anything. Anyone have any suggestions? I am running out of ideas, unless the distributor gear or something like that went to crap on me.