Won't run past 3500 rpm

[ford38v8]

THat's a beautiful engine, I bet you spend lots of time admiring that honey!
Your description of what you've tried sounds like you have a fuel issue, and from the picture, I see several possible causes:

Your high vacuum together with the small air filters suggest an air restriction. Try a temporary removal of the air filters for effect.

It takes only a very small air leak to lower your bowl level to the point of lack of fuel on acceleration. The fuel pump's glass bowl should have a cork gasket soaked in oil before careful installation. Also, check the tightness of those worm gear clamps.

The inline filter is redundant with the glass bowl, and may be clogged anyway.

Your rubber flex line may be collapsed internally. I would change out that line to a Shewman fuel resistant line, advertised in the V8 Times, without check valve.

What is not shown in the picture is your tank to firewall fuel line. Original lines being copper coated steel, they rust, flake debris, and develop pinhole leaks. Not cheap, but a Cupronickle fuel line is a great solution to many issues.