RE: Importance of engine break-in ?
NF,
None of the run-of-the-mill production engines are pre-run at the factory.
Most are produced with CNC, so you can be sure the fit is very good and only a minimal amount of break-in is necessary.
The only engines that are pre-run, are probably those made by Jett, Nelson and other competition engine companies.
They are run prior to being broken-in, to verify they will perform within spec...
Also, some intricate engines; such as multi-cylinder, very dear units, are also pre-run, to ascertain they actually work.