From the blade side, the XL-100 resembles the conventional circular saws of its day. The gas tank and front handle are the only give-aways that it's somehow different. This is what the saw looked like before Tony restored it. To give you a sense of how rare these things are, when he bought the saw on eBay he was bidding against 15 other people and had to pay about $600 to get it.
When viewed from the rear it becomes clear that this is chainsaw motor with a base plate and circular blade housing attached.
This saw is in better shape than the last one. The photo was provided by Wayne Sutton, the owner of Wayne's Chainsaw Museum in Amboy, OR. From the back side it's evident that this is a chainsaw with a baseplate added and the bar removed.