Probably the best and most consistent CS engines were the 2.5cc (.15 cu in) Silver Swallow diesels. That doesn't do much for most of the stunt commuity, however.
I've heard that some of their competition engines - if you're willing to get several to find parts to put one excellent one together - can and have set various records. Again, not much use to the CLPA crowd. Kinda makes an $88 engine more like $500, and still might not be quite what you want. Don't even THINK about replacement parts, either.
I've heard the many of the original run of Silver Swallow .15s were part of a Mainland (Chinese People's Republic) government program to train machinists. Most of them, according to the papers in the box, were built within a fairly brief period. Ed Carlsen imports a recently produced CS .15 diesel, near identical to the SS except for brand marks. The one I've seen is much more nicely made than the main run back in the 1950's or '60's.