Radiator Cap Won't fit into the grill shell

[Robbie Horn]

1931 Coupe. I purchased a shiny new chrome radiator cap for my A but it won't fit into the grill shell. It has a lip on the bottom of the cap that is too large for the hole in my grill shell.I found one online at The Early Ford Store in California that would work because it does not have a lip but they are out of them & don't know when they will get some more. I'm currently using a radiator cap that was on the car when I got it. Has anyone else ran into this problem?