Where can I buy a motorcycle engine build kit?

rev tech make a complete motor just like S & S,however I cant vouch for it.You can also do it a component at a time say with cases from Delkron,flywheels from S&S,carillo rods,wisco pistons and so on. Thats how I built my panhead.Get the catalog from the guys at Fog Hollow and you will see how you can build your entire bike without a single H.d.part in it.