Oil pressure light at higher speeds - Eagle

Good oil pressure at low RPM but not at high RPM tells me that either your oil pickup in the oil pan is plugged/restricted, or the oil drain passages that drain the oil back to the oil pan from the cylinder head are plugged/restricted. 

This happens a lot on Eagles because of the plastic valve cover. The valve covers leak a lot, so people paste obscene amounts of silicone sealer on them in an attempt to make them seal. The sealer breaks loose and plugs things up. 

I've had this occur on 2 AMC 6 cyls, 1 a 77 258, the other an 84 258.  in one case, it was the sending unit, in the other it was the drainback holes in the head being sludged up with broken umbrella seals, and a heinous amount of blue RTV from the PO trying to seal up....you guessed it...the plastic valve cover.  I've never had an AMC 6 oil pump fail me, nor have I ever had an oil filter on an AMC 6 clog up, but that's certainly not out of the realm of possibility.

So I do agree with several of the other suggestions - swap out the oil filter, put in a new sending unit, check your engine ground strap, and if the light still comes on at speed, I'm going to go with 99.5% certainty that most of the oil is sitting inside the valve cover at high sustained RPM due to the drainbacks being clogged with crap.  Another good clue to this possibility would be an air cleaner full of oil from the valve cover breather backing up and letting excess oil get pulled up into the air cleaner.

So I've never seen any reason to do amy sort of mod to any AMC 6, and frankly, on the 8s it's just a matter of attention to detail. Maybe that's my secret - all of my bosses over the years in every case on every review I was rated high on "attention to detail" - sometimes it drove them nuts because things had to be perfect, but hey, like my wife says - if it's worth doing, it's worth doing right. 

So I've had no reason for any restrictions or mods on rocker arm oiling (again, other than EARLY Ramblers, but then even AMC talked about that)

IF the engine is right and in specs and things are as designed, there won't be issues like this.
The OP is dealing with a fault, something wrong, not a design flaw, so has no reason to modify anything, only check the pressure with a gauge, etc. (we have had a couple of guys talk about filters coming apart inside, so we did mention "could be filter)

IF there's "too much oil" on top, then there's a fault or issue somewhere that needs to be fixed, causing that oil to stay up there. 

Aren't the new lifters for AMC engines a thousandth or so smaller than the original lifters and allow more oil to leak between the lifters and their bores? I seem to recall seeing that somewhere. Of course, worn lifter bores don't really help and not too many people are re-machining the lifter bores in their block to fix that.