As stated, it's almost undoubtedly the Plenum gasket. No need to pull the engine, just remove intake manifold. But again, as stated, I'd hesitate to put the money into a Hughes kit and more importantly the labor to install it without doing a compression test on the engine with that many miles first.

Hughes Plenum kit will fix the oil and power loss and should also improve mpgs slightly as you won't have to give as much throttle to accelerate. Nothings gonna really improve gas mileage a lot on a 5.9 V8, at least nothing that wouldn't cost a lot more than the savings would see. It is what it is. The engine reminds me of an A 10 Tank Killer. Big, slow and guzzle gas, but aside from the design flaw of the Plenum, you almost can't kill it. The LA 360 was basically designed in the late '60s when fuel economy wasn't even an afterthought.

As for the headlights, I've found that cheap, white, gritty toothpaste will do as much as those expensive kits. A good stiff brush and a little water. Then wax them, synthetic wax with strong uv inhibitors will keep them clear...

 

Whenever you do the plenum that would be ideal to do the timing chain also. Checkout lmc truck for dash parts.
http://www.lmctruck.com/dodge/

I think it's safe to say you like camo!

 

Nice truck lady.
Except the antlers. Really. Cheesy.
As far as lighting goes, look into http://www.nightriderled.com/driving...545/n1545.html