RE: o.s .25xz break in procedure
You drive the car. Keep it leaned just below max RPM and drive the car at varying speeds, up to full and down again. Gradually work the high-speed needle towards peak RPM. If you can accelerate up to speed and the RPM will hold at full throttle, you have the mixture OK. If it accelerates up and sags, it's too lean.
Anyone who claims to break in an engine by idling it for a few tanks' worth is not breaking in their engine, but breaking it. It won't last very long if you do that. The engine must be run under load.