Gas Tank Pressurising

I have a 71 Satellite running stroked 340 - Manual fuel pump,750DP holley and running a return line via a regulator.
After only 5 mile run I have fuel leaking from the vapour tank under drivers rear quarter panel,Vapour tank is rusted.When I removed the fuel cap it came off with a lot of pressure (if i hadn't had a good hold on it it would have shot across the garage) also a loudish pop as the fuel tank went back into shape!!!
It has the original gas tank with 4x breather pipes exiting on the drivers side .
I'm being told to drill a small hole in the Gas cap and to block off or loop the four breather pipes????

I would obviously look in to checking and unblocking these 4 breather pipes to make them work again as they are there for a reason.
Drilling a hole in the gas cap will solve the issues as well, but 1) do you really want to cause a leak there? 2) Original vents are re-routed below the car for a reason, now you creating it to vent highly combustable gasses pointing at yourself!

Having a similar problem with a Coronet. Turn off the engine after it runs for awhile. Wait 1-2 minutes. Gas begins dripping out of the vent hose that runs up into the frame. Remove the gas cap and the leak stops. I have blown out the hose.

My 73 has a 4 into 1 vent manifold in front of the tank.

There is a brass shuttle valve inside the line that goes to the vapor canister under the hood.

It was stuck and caused the tank to pressurize, blowing the cap off when I unscrewed it.

I had to carefully cut a section of the manifold off, then carefully drill out the valve while not damaging the line, than weld and JB weld the patch back in the manifold body.

Now it's continually open to the canister, but does not pressurize the tank and no open system fumes.

The only thing I lost was over fill protection.