"btw , boring is done with a boring bar!!!!"
Um, yeah... But the bar can be driven by a fixture that self centers on the existing bore centerline, or it can be attached to a machining center that can locate the bore centerline where ever you need it. Correcting the factory mess to actual blueprint spec(if you haven't had it done on a block machining center you probably don't know how bad factory is...), or offsetting to increase wall thickness on major thrust, or to avoid sleeving. It's MUCH more accurate. Offsetting .015 will not hurt anything, and costs nothing more. Sleeving will repair it properly and permanently, for another $100 or so.