Okay, I've had a couple of collector's either e-mail me or reply to my posts on facebook saying this tank was originally made by Payton as a load for Lionel flatcars in sets carried by sears and J.C. Penny's. When you pop the turret off, their is a small, raised letter 'Q' close to the gun and to the left as you're looking at it. Both of the tanks I currently have in my collection have that 'Q'. Also, the hulls are 5" long while repos tend to be shorter - 4 7/8" long. Apparently Payton would supply the tooling to anyone for a fee. Perhaps Remco bought/rented the tooling from Payton and re-packaged them with their own header bags.
Enjoy! Opa Fritz and Oma Bettina