I have the HO version and I just measured the outside diameter of the pit and used a router on a trammel bar to rout a perfect circle. If you don't have a router or access to one, I would suggest laying out the circle on the plywood with a trammel bar (a wood yardstick with holes in it for a nail and a pencil) and then cut it out with a jig saw using a fine wood blade. Cut it as close to the diameter without going too large (diameter) and you can file or sand it to final size.
Life is what happens while you are making other plans!
Bob, is that Bantrak as in Baltimore Area N Trak?
Lee
Route of the Alpha Jets www.wmrywesternlines.net
Lee,
It's in 1/2" plywood. I had thought about changing the original and depending on my options I may still do that. There are multiple things that have to be changed though so I was avoiding that option for now. Hadn't thought about taking it to a copy center but it's worth giving them a call at the very least. Appreciate the tip.
Bob
First question, what are you installing it in? Some materials are more forgiving than others. For plywood, you'll want to be pretty precise, if foam, you can nip and tuck as needed. Mine's in plywood/homasote sandwich, so the plywood is cut a little loose, and the homasote fits more snuggly.
You could simply measure the diameter of the base and use a string anchored at the center and a pencil to make your own.
You could also take the file they sent you over to your local copy center and see if they can print it out for you full size.