I used fairly thick cork gasket material liberally soaked in shellack to stop my gas gauge from leaking. I tightened it down slowly over a few days and no leaks so far.

The gasket I am using does not require the glands or rings as it is located by the studs. I assume the engine rebuilder tossed the glands and rings as there were none when I took the manifolds off. I am familiar with the issue you are describing as Model T Ford manifolds use them and at one time a parts supplier was reproducing them incorrectly so they were too proud and the glands could not be compressed.  First question, Is my recollection that Plymouth used glands and rings correct and if so is there a source for them?  I can make up the rings but not the glands. I can't believe I can't remember if there were any when I took the engine apart and brought it to the rebuilder.  But, then again, these days there are times when I can't remember what I had for breakfast!

Those gland rings can be a problem. If the new gasket is thinner than the designed one the rings can keep it from being compressed and cause leaks. They don't seal anything they just help line up the manifold & the block. When you have it apart again put it together with no gasket and see how much gap between them and your problem night be easier to spot.

Thanks Chet but I am running a Carter BB-1 carburetor and I tried swapping it for one from one of my other cars that ran fine when I first had the problem with no change so I don't think the issue is with the carburetor.

John,

There is some info at the bottom of this report that details what I did to get the gauge working without leeks.

see link to info: >>>  Feb 14, 2020

Chet...

You know, I had this exact same problem, but I don't remember exactly what caused it.  You are correct it is vacuum. I think it had something to do with the acceleration pump on the carburetor.  Mine is a RT-08 Carter.  Do you have another carburetor to troubleshoot with?  I'll look back on my adventures and see if it will jog my memory, but I believe something loose on the carb caused more air to mix with the gas.  I keep thinking the acceleration pump was loose and sucking air.

Chet...   

After a complete engine rebuild I am fighting what I believe is an intake manifold leak.  Car starts right up cold with full choke but will not idle when the choke is all the way in.  The idle picks up when I spray WD 40 around it which I assume suggests that it is a vacuum leak that I am trying to chase down.  The problem is that I have had the manifold on and off twice using a new gasket each time both on the block and the intake manifold and the problem still exists.  The carburetor (Carter BB-1) was never an issue before the engine rebuild but I did get back into it to make sure the float level was correct and it was. I even swapped out another intake manifold I had with no change.  The gaskets for the exhaust manifold I have been using are a one piece affair that includes the intake manifold gasket and I am wondering if that is the problem. It's been a long time since I took the engine apart for the rebuild and even longer getting it done but I vaguely remember that there was a gasket on each side of the intake manifold and that there were individual  glands and rings on the exhaust ports.  The rebuilder reassembled everything using a new gasket set he ordered and discarded the old stuff.
 Has anyone else dealt with this issue and managed to deal with it successfully?  Is my recollection correct and if so can you still get the glands and rings?  Car runs great with the choke half way out, go figure!

If a surface is rough I have used JB Weld to fill it in. I put waxed paper on a flat plate or just waxed the plate and screwed it down with the epoxy between the plate and the rough surface. Let it cure and when it's hard remove the plate smooth up the edges with a file. Then it will hold a gasket a lot better. I had to do both sides of my thermostat housing and water neck that way. If your gas gauge doesn't seal with what you have this might be a idea. Our car has no gauge just a plate blocking the hole. I have thought about trying to fit a boat gas tank gauge in there but think about it is as far as I have got. 

We moved to the Birmingham Alabama area to be closer to our oldest daughter. We live on top of a hill with a steep drive. My gas tank gauge leaked every time I drive up the hill, so have been trying to seal it better. I have found a supplier of vitriol gasket material that is impervious to gas. I am trying that with some fuel resistant Permatex MotoSeal gasket maker and a newer product Permatex Permashield gasket dressing.

My original tank had a long neck supporting the gas gauge and leaking was not a problem, but I had to replace that tank many years ago.

Anyone else have this issue and solved it?

The spring arrived today. It looks a lot better than the one I have in the valve now. I'll change it out before we drive the car again!