I'm still working the blowby issue on my 83 F100 4.9. The sparkplugs are all free of oil. No smoke in the exhaust.
The oil fill cap on the valve cover was loading the breather with oil and letting oil drip down from the fitting on the breather. I put a regular solid cap on instead of the emissions one, and it still leaks oil out through the gasket of the cap, even though it's on there tight.
The pcv valve seems to be fine, no leaks around the valve cover opening, and I tested it it opens and closes. The hoses are hooked up as they should be.
I had a leak at the bottom rear of the pushrod cover, so it just got a new gasket and reinstall. I was getting 1-15 drops of oil on the driveway, and it just started leaking now from the front area of the cover.
I wonder if it is pressurized like the valve cover from the blowby and that's why the gasket won't hold? My other question is on the valve cover and using an unvented oil fill cap. Isn't the pcv valve handling all the pressure? Why do I still get oil pushing through at the oil fill cap?

 

It sounds like it's producing more blowby than normal, so the pcv wont handle it. I would do a compression test on each cylinder. Worn rings will produce excess blowby. Is there a good oil change history?

 

It was neglected by the previous owner. I need this 300 to prove it's bulletproof.

I thought the bad rings would leave oil residue on the plugs.

 

I'm thinking blowby is a vapor, will slip by before oil will, but I'm no expert.

 

Your motor is worn out. It either needs new rings, or new rings, oversize pistons, and a re-bore out to .020 or .030.

A compression test to check compression will tell you what kind of condition each cylinder is in. Pour a little oil in the cylinder(s) with low compression and check the compression again. If it goes up, you've got bad/worn rings.

For instance, my 300 has the following compression (If I can remember the numbers right, it's been a while since I checked compression):

1 - 151 PSI
2 - 150 PSI
3 - 127.5 PSI
4 - 126 PSI
5 - 101 PSI
6 - 126 PSI

Bear in mind, my motor has signs that it'd been overheated. The valve-train is worn out all through the motor (has new pushrods, rocker arms, and lifters, but I need to get a longer push rod for the #6 intake rocker where the cam lobe is slightly worn down), the radiator was brown up to the top, the doors had mud in them, and the top of the engine crossmember had mud and grease all over it. As well as the fact that mechanical oil and temperature gauges were installed, the upper radiator hose that's on it looks like it's the wrong hose and was put on there as a "temporary fix". I think there were a few other signs, but you get the idea.

Thinking about it further, you could tell my motor was overheated if you looked at the compression carefully. The #1 cylinder on water cooled engines always runs the coldest and typically has slightly lower compression than the rest of the cylinders in a healthy motor where it doesn't run as hot. This is the cylinder with good compression. The further you get away from the water inlet near the #1 cylinder, the lower the compression gets because it got hotter towards the back of the motor.

My motor runs good, starts good, has plenty of power, and may or may not have a slightly cracked head/slightly damaged head gasket (uses a little coolant, it seems). It doesn't smoke through the tailpipe, but I had to install a soda bottle between the air cleaner and breather on the valve cover to catch the oil that comes out.

For what it's worth, stick a catch can on your air breather running to your air cleaner like I did and keep driving it until you can rebuild it. It won't hurt anything. Just keep an eye on your oil level.

 

Thanks for the replies. I've had a small coffee can catching the blow by, looks like a rebuild or another motor is the solution.