The CS-4400 and CS-510 are the basis for the BME 44 and 50cc engines. Brillelli is uusing the CS-520 for his 50cc engine. Looks like the engine is gone from the BME page but I am attaching two I found on the web showing the adapter someone else made. You can make or maybe try to buy one from BME the aluminum adapter. He may sell you the prop hub too. Keith is a good guy and easy to talk too. Basically you need a piece of aluminum bored to fit over the spud in the block. There are 3 set screws in mine as I remember to hold it to the spud. Also used a sealer also before I attached it. The carb spacer block bolts to the adapter. You need 2 tapped holes on the face of the adapter also for the spacer to bolt to. The engine I made is in my son's Hangar 9 Extra 260. Awesome power.