The mechanical fuel pump in actuated by a cam on the crankshaft. If the motor is turning the pump is being pumped. The gas is therefore sucked from the tank to the carb after going through the filter. If you have air in the lines there will most likely be a bubble in the filter that is difficult to get rid of. Eventually the bubble will work its way out by that air being absorbed into the gas. You might want to disconnect the line somewhere after the fuel filter and hold it lower than the tank to allow gravity to push gas into and through the filter to get the air out. Then cap it off with your thumb and reconnect it.

I suspect the "tank coating" (particles) are going to plug your filter for a while until it sets up tight. May have to change the filter again, and again.

I assume the float level, needle valve / seat are A-OK?

Not a big fan of glass inline filters, they are dangerous. But in this case it helps you see whats going on.

if a fuel line leaks a little will suck in air . carb should have a filter behind fuel line intake spot on carb filter and spring

Marv has a great answer and something to check for sure. Some of these older model trucks also had an inline fuel filter at the base of the carbureutor where the metal line screws into the base of the carb, the filter sits inside the brass coupling and is made out of porous brass itself, they were notorious for getting stopped up as this was the only fuel filter original to the truck if equipped as such. I would definitely check for that!

Don't worry about the air bubble in the fuel filter. It's not an issue at all especially if the engine runs fine. In the early years as your truck is, the fuel filters were near the carburetor to that you could see the condition of the fuel filter. The size of the fuel line (3/8" rubber vs 1/4" metal) doesn't matter. They both have about the same inside diameter - the important measurement for fuel flow requirements.

I have a 55 Chevy truck that I was having problems getting started. It was not getting fuel. I took out the tank and cleaned and coated the inside. My inline fuel filter still showed signs of particles so I took off the fuel line and changed it to rubber fuel line. After doing that I no longer had problems starting like I had before. The rubber fuel line is 3/8" diameter and the metal one was way smaller. Not sure exact size. The truck was starting and running fine. I went to check the fluids the other day and I noticed with the truck running the inline fuel filter was empty but fuel was trickling in the inlet part but not enough to maintain a filled or even a half filled filter. Is there any input on this situation as to why the inline fuel filter is not holding any fuel. I wouldn't think the size of the supply line is a factor considering that the mechanical fuel pump pumps the same psi of fluid at all times. I would appreciate any input and I thank you for any and all assistance.