I have a 55cc chain saw conversion that I bought and haven't used. The guy I bought it from wasn't sure what it is. The conversion is a very professional job. I want to sell it and I'd like to know exactly what it is before listing it. I have confirmed the size by measuring the bore and stroke. Since I bought it I have gotten input that suggests it is a Stihl conversion. It came with a Byron purr-power mount so it had to be mainstream enough for Byron to make a mount for it.

Anyone have any ideas?

Here's a picture of it.