The Wilcox-McKim is a rare bird, even though it sure looks like a Spinaway in many ways.
This example bears a tag that states the company was based in Saganaw, Michigan, while Spinaway company was headquartered in Freeport, Illinois. I suspect that the Wilcox-McKim was a badge motor.
The primary differences between the two were the gas tank and the exhast manifold. The example below is a wonderfully original motor.
