From my research so far.... Of what seems to be the biggest 3 suppliers of VW aero engines, two offer kits: Great Plains and Aeroconversions. Hummel engines offers only complete engines and, for the same displacement, is lower in price than the other two even though assembled. The other two will assembly them for you, for a price. Since I am interested in building a Hummel H5, the Hummel Engines are inviting. Another option is to buy a case and all the required parts 'piece wise'. Essentially putting together your own 'kit'. I have seen a brand new block on ebay for about $750. And there is also the possibility of scrounging around and finding a used case at a scrap yard (but does it have any flaws?), or a lower price new case at a VW shop (not on ebay). What are the pros and cons of each method? How many of you build or buy? And if building, where did you get your parts? How difficult is it to build?