I have a 1980 sachs prima with the 504/ motor that I am currently in the slow process of completely overhauling. I've upgraded the carb to a dellorto 16mm and now I want more. I was going to by a kit, but this bike really has a lot of miles on it and dont really want to deal with rebuilding the clutch and replacing bearing, etc... My question is then, does anyone know of any replacement motors that either drop-in or even require a modified bracket or something? I am not very concerned with it being original, and this would really help me out! Thanks.