Purchase two gauges of like sizes, here are two that I quickly found, but you can do better. One is the Smiths
Oil Gauge, the other is an Air Fuel Gauge. Remove the faces from both gauges. Then carefully razor the cardboard logo of the Smiths face of the gauge and place it behind the AF face that you have razored open. Use a small paint brush and Testor's model paint to match the needle. Shouldn't take you more than an afternoon. If you're careful, nobody will be able to spot your work without really looking hard at it. And, even then, they won't know for sure.
Remember, creating a "window" on the face of the AF gauge and then placing the Smiths cut out behind so it "peeks through" will give you a cleaner look.
