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Not sure how many miles the rebuild will last; it depends on how tight the tolerances of the machining were and how well a job the machine shop did. Was it rebuilt by a small garage with a good rep or a service dealer?

As far as break-in procedures makes ure you follow specs to the T, not doing that of course will shorten engine life. Some others might help me out here but I am pretty sure break-in should be done on natural or blend oil (not full synthetic) for xxx number of miles so the rings will seat properly. Again I do not know the figures but that is what I heard.

But if you have a freshly built engine I would swap over to full synthetic (worth the 4-5 bucks a quart) post-break-in time. I have used Vavoline Syntec on my previous car and it was great. I have heard others on here swear by Mobile-1's synthetic as well, but I ahve never tried it.

For further reading on Motor Oil as well as other fluids:
http://www.vfaq.com/mods/fluids.html