Dumpstercrusher, I also bought a 'built' engine and it has been the most reliable part of my bike. The standard Chinese accessories that came with it fall very short by comparison. Slowly replacing them!
It sounds expensive in comparison to an eBay kit, but if you count the custom machining, assembly, design and overheads into it, it is dirt cheap and could only really be done as a labour of love.
I'd do it for a living if it were otherwise.