I've got one of them sitting around here somewhere.

Problem I ran into is the needle bearings on the crank. You can make a thrust washer from bronze, and install between the crank and bearings.

You can also have the case machined on the prop hub side and install a regular roller bearing on that side. No need to bother with the back bearings.

Lot of work for a 35cc engine. Personally, since I don't have the mills and lathes for makeing my own parts; I don't bother with anythihng that I can have done for a reasonable cost $$$ by someone else. IMO, making bronze thrust washers or milling the stock case to accept a roller bearing- is too costly for the intended purpose. IMO- the whole point to a conversion is that it's cheaper than a DA or ZDZ. Spending a bunch of money on machine work is not the idea behind the conversion engines.

Craftsman makes a 38cc engine that practically converts itself. A Ryobi 31cc engine can be converted in about 1 HR- once you've gathered all the parts.