[jlsanborn]

I know this is little old and you've already installed valve cover vents but I thought I would share in case anyone else stumbles across this in their searches.

I also have an early 327 and will also run the script valve covers. Fortunately, I have the block mounted PCV connection. If I didn't, I would drill and tap the back of the intake manifold and fab a baffle to keep oil out. By simply installing vents you've eliminated the crankase pressure that would lead to oil leaks but you have not provided any fresh air circulation to combat the sludge issue. Ideally you'd want fresh air entering one side or one end of the engine with the exit being opposite. I would also suspect messy oil film/mist around your vents as they are the escape way for all the crankcase gasses.

EDIT- Just noticed that you do have a connection to vacuum, but no PCV? I'd think that would be drawing a lot of air (most probably right from the vented filler cap) giving you a lean condition?

Nice truck man!