I've got a model 15A. Great skidder! The original engine was either a gas or diesel 172 cu. in. Ford industrial engine. Ford sold those engines by the boatload back in the day. They were used on the ford 900 tractor, the ford 4000 construction tractor, stationary power plants and a lot of other applications. If you got another engine lying around, you could pretty easily fit it to the machine. The transmission is a common one as well. Contact Garrett Enumclaw co. And leave a message with Adam Garrett, he will let you know if he has a lead on something, or will otherwise be able to help you.