A thing to note about 'diesels':

The combustion impulse is different from both methanol and gasoline based fuels. Combustion timing is directly controllable by, first, the balance of compression and mixture settings, and somewhat less by prop and fuel selection.

Most 'sport' diesels I've run and seen run were able to find a "sweet spot" setting with much reduced vibration compared to higher/lower compressed, and/or richer/leaner settings. That setting seems suitable for sport flying, and (on decent fuel) was quite dependable.

My interpretation: The dynamics of the combustion impulse interact with the "native" metal-bits vibration tendencies. This often reduces the need to tinker with things like shaft balalnce, counterweights, etc. Special purpose, high-RPM 'diesels,' of course, are another beast entirely.

The ChiCom Silver Swallows were (are, as CS, with updated tooling) mainly sport-use engines. A bit noisy, due to the type of exhaust and bypass porting... But, still, very useful for the intended purpose. That purpose was, originally, training machinists, btw. Useful, without great internal tinkering. They are not high performance engines, but still nicely strong, and serve well, once you learn to find the "sweet spot" and fly with it.

Like the Fox 35 in this one narrow way: Both engines were designed to be "centered" and very tolerant of QC while still capable of their intended purpose. Some recent CS .15s (Silver Swallow, the next generation) were far better made than the original batch of Silver Swallows - which means only that a longer and more conscientious break-in may be required for best use. Neither 'generation' is/were Kleenex engines (to use once, then toss).

These engines can be well worth their price if we learn how to use them for their intended purposes. Silver Swallows, old and new, and Fox 35s still can do what they were meant to do. ...If we let them...