Ok, I just got the plane out and measured the space for the fuel tank. There is room for a tank about 2 inches tall, 2.5 inches wide, and up to about 4 inches long. That's leaving room for foam rubber around the outsides too. The engine is a Fox .19 from the '80s, I think it should be happy with 6 ounces of fuel, but if an 8 ounce tank will fit, I guess I'll ahve a little reserve on hand.

Whatever will work is fine. Thanks!
Keith