I did some searching for the fuel tank pick-up tube, and boy, it might be difficult to look inside of it or clean it using the filler or sender's openings (if this is my case) without removing the tank and/or opening it up. I might try to blow compressed air through the main feed, and then inserting a hose with my vacuum oil extractor tube to pick up any dislodged pieces? If this turns out to be the clogged mesh sock, I might just get a new fuel tank. The local radiator shop quoted me $400 to fix my original copper 280z radiator. Back in CA, I had shops doing it under a 100. I can't imagine how much they would ask to open/clean/re-weld the tank...

I am getting ahead of myself, I need to keep positive thoughts. Here are some pictures from: https://www.classiczcars.com/forums/topic/67550-most-dreaded-of-jobs-finally-on-the-horizon-the-fuel-tank/page/2/

I did the return line restriction test - the fuel pressure went over 60 psi (max on my FP gauge). I have a spare Chinese FPR knock-off I used to have, I can replace the Aeromotive with that one.

I need to rig up a temp fuel canister and try running the car off it. If I have an occasional fuel restriction in the tank's fuel pickup area, that might explain all these issues. I also considered pulling the drain snake down the main feed fuel hose/line inside the tank to see if it clears anything. Although the thought of a piece of debris in the future causing a break-down on a side of the road is not 100 percent comforting.

Since you're set to 3 bar maybe consider finding a factory OEM 3 bar regulator. 3 bar (43 psi) is common. I remember going through the search for an adjustable FPR, even buying an Aeromotive unit, but finding that the aftermarket units all leaked down rapidly. I eventually ended up with a late 70's Porsche style Bosch adjustable FPR that I modified to use a vacuum reference. It was fun.

Anyway the OEM FPR designs just have a better seal than the aftermarket machined aluminum units and they're designed to last 100's of thousands of miles. Worth a consideration, I think.

I hope this saga post is over.

I tested the fuel pump running off the fuel jug and it worked without any hesitation, the FPR maintained the 43 psi of fuel pressure. I dropped the fuel tank and found very fine sediment of rusty 'sand' at the bottom. I couldn't fit my endoscope into the fuel bowl to check the condition of its sock, but I think it is covered with crap creating major flow restriction for my pump. I took apart my 100 micron pre-pump fuel filter and didn't see any sediment inside (good news). The sock did a decent job preventing rust particles from getting into my fuel filter and pump.

I bought the s30.world early 76 fuel tank and it is a piece of beauty/construction. It is an exact replica:

I also replaced my evap fuel lines (they looked old and stiff, but with no cuts).

It took 12 days to get the tank, s30.world has a warehouse in the States, no import tariff BS fees. I just wish the web site would send a tracking email. I contacted them directly and haven't heard back. The tank was also very nicely packaged in a sturdy box.

I did initial fine tuning of idle in my TunerStudio since now I have a good fuel pressure.

Thanks to all of you who contributed to the ideas.

Those tanks are amazingly well built. I didn’t have any issues reusing the bumper pads from the original tank. Contact cement worked well.

Yes, my original bumper pads were in a good shape as well, reused them. I applied the double sided 3M sticky tape to hold them in place.