Hi Jetsky,
The Mac above is a 38cc. The one that you have I think is a 33cc like mine. Here is a picture of mine. I has the front carb. It doesn't have brass spacers like my Homelite XL 26cc. The thrust bearing issue is what I am working on with both these engines. I think that the 33cc would fit a GB Ultrimate and at 3 and !/2 pounds ready to fly it would be light too. It has needles bearings at both ends of the con rod. My XL 26cc has a plain bearing on the small end of the rod. Lets keep this thread going with progress on the Mac's.

Dave