I have the exact same Jeep as you. I just went to the dealership and bought new CCV replacements. They only cost like 30 dollars. Like you I had oil blowback in my airfilter. Replacing ALL the CCV stuff solved the problem. My oil guage also didn't seem to be reading correctly either and I found that the oil level sensor had gone bad. This also an easy fix and the part isn't too expensive from the dealership and its reccomended to use the Mopar sensor from DC. A sign the sensor is going bad is that it will leak oil onto the oil filter below it.
I had this problem on my 86 4.0. I removed all of the small plastic factory tubing, replaced the rear elbo with a 3/8" brass elbow, and ran 3/8" fuel line over to the airbox. I then capped or plugged all of the other holes from the stock system, it worked like a charm. I even think it ran a bit better, but am not certain.
The rear elbow that you drilled out is now probably out of spec. It has a fixed orifice of a calibrated size which is supposed to meter (limit) the amount of crankcase vapors drawn out of the engine. The orifice can be cleaned out by pushing the end of a paper clip through it, but it is not supposed to be drilled out by a drill bit larger than the orifice size. Get a replacement from the dealership, get new grommets for where the elbows enter the valve cover, and replace any old rubber tubing that may be hard and cracked. None of this is very expensive.