I run my lapped iron/steel engines as rich as it will run without glow support for the first start. Run 2 minutes and cool off. I run one full tank doing 2 minute intervals at the sloppy wet rich setting. For subsequent tanks I lean it out 500rpm at a time for a half dozen 2 minute intervals each. After a half hour I run a couple tanks at the 2/4 break where it occasionally hits a 2-stroke run. After about 45-50min I'll peak it and Richen to about 800-1000rpm off peak and run it there for awhile. Once the piston will roll to BDC on its own, I consider that pretty close to broke in. If that makes sense. I'm known to go overboard with things, so you may consider my method extreme.
I usually use 0% nitro and 20-25% castor oil fuel. After break-in, I'll use 10-15% nitro 22-25% castor oil.