Puking Gas !!!

I'm pretty sure the Layson's modification is to install a flat plate that splits the tube in half, like a modern filler neck. Then the liquid follows along the bottom half of the neck and the entire upper half becomes the vent.

They also baffle the neck, like the upper portion of a modern neck (the part with the little hole and the door and vent hole) to keep the gas from flowing up the tube and out onto the 1/4 panel, as the neck angle is too shallow and allows gas to run up the neck on sharp right handed turns.

The last fix you should be doing is also to install a new filler neck grommet, as these are a common sourse of gas leaking out when the tank is filled above 1/2 way.

All not hard to do, but I would think the baffle at the top would be the hardest part to accomplish, and maybe sourcing this piece from a modern filler neck and installing it into yours would be the best bet!! Geof