What is the diameter of the fresh air cowl vent opening?

Looks like you need to do some fixin' but how are your vents? Often the door hinges are rusted and they will break if forced. Good usec ones can be found with a parts wanted thread here on FABO.
Thanks ToolMan! I rebuilt both the driver's airbox and heater box using about everything in the garage; epoxee, fiberglass, JB Weld, old cabinet hinges, bubble gum...

I'm wondering now if I can lose the brim on the top hat and just have a 2" tall X 5 7/8" dia, 16ga cylinder made, and then tack weld it in place so it wont fall out and fill the seam between the cylinder and air duct opening with one of POR-15's bondo products.