i was just checking out a amc forum i saw this and it might help both of us a little.
I'd say this is a typical oil pressure reading from an AMC V8 after the engine has suffered a cooling system failure. My suspicion is that the iron oil pump gears inside the aluminum housing are fine during normal temp heat cycles, but when temps go too high the thermal expansion rates become incompatible and the clearances get loose; it seems the gears chew into the aluminum housing surfaces. I've even noticed the lips of the iron gear teeth even get ground away, having an irregular notchy look from biting into the aluminum case. More severe, when this happens to the oil pump, the next thing is you'll hear bearing noises, probably from the rear main and rod bearings. (don't overheat the AMC V8) An AMC V8 like this is likely to throw a rod (usually the 5/6 journal, more rare 7/8 for some reason) if sustained high rpms are demanded from it. (It'll still run fine for hundreds of thousands of miles otherwise). 20lbs of pressure at idle, in my experience, is normal for the AMC V8 that hasn't been overheated. First off, I'd say to go to 20-50w oil and filter change to continue running engine for street duty -but avoid high rpm if you notice bearing noises. Second, you might be able to restore better pressure by servicing the pump on the engine. Remove oil pump cover/filter adapter, inspect gears and housing. If the gears are worn put in better ones, and if the cover is scored restore the surface to smooth. (See
amc oil performance mofication setup) -I'd say the low oil pressure is usually a combination of a loose oil pump and worn bearings, most likely from a cooling system failure- Fram used to make one of the best oil filters for AMC's, along with AC/Delco, but Fram was bought out (I think in the mid-nineties) by another corporation who cheapened the oil filter product line to a lower standard. Apparently TRW was part of the deal, and now their forged aluminum pistons for the AMC V8 are become unavailable -good pistons for a high rpm
AMC 304 /360 if you can find 'em though; I've used 'em in a 360 built for 7200 rpm cam and kit and they were flawless. (I used the Iskendarian cam and kit with Rhodes variable lift anti-pump up lifters and it worked great for me; smooth idle and wild "drool bucket" high rpm power!) OK I'll shut up! -great work guys on this AMC Forum!
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)that had 110 miles on it. I went from 0psi to 50 when I replaced it 
If that is not it it might be your pump inside your oil pan, you will need to drop your pan and replace that. If that its not it, it might get more complicated up in your valve cover....Good Luck!!!!
