This has been linked here before, but...http://www.mototuneusa.com/break_in_secrets.htm
I found this lnk ages ago when surfing. I followed this method when I broke in my new engine. Because my new motor A15, is bigger than the old a14, (129cc's) I jetted it really rich.
I towed the car out to the countryside, and let rip.
Once it was warm, I pushed my brand new engine, up to 105mph. (On the clock) Being towed home, I phoned the tow car driver to check my speedo, and it turned out it was reading slow by 15%. So I had pushed my BRAND NEW engine to 120mph @7PSI.
No problems. That was holding back a bit too!
It sounds like your engine builder should know his stuff. Did he bore some extra clearance into the bore? My machinist gave me an extra three thou, to allow the piston to grow a bit more from boosted tempratures.
The suggestion of a gas anyliser is a good one. I recently borrowed from a mate a broadband air/fuel ratio meter. I put a boss on the tail pipe to fit a five pin bosch O2 sensor. You plug it in, and tape it up the boot and in the window. Then the remote plugs into the cigarette lighter socket. It's got a digital display which tells the a/f ratio.
It told me I was running rich as. I used it to diagnose why it goes flat at 6000.( Leaning out, not a spark problem)
If you can get a hold of one of these, you'd find it most helpful.