318 build
I'd like to see your dyno slip after it is built and then you can tell us if they lied or not. A lot depends on who you ask if the rag's lie about there builds or not. Some say the rag fudges the numbers so the parts look good for the advertisers. I myself do not believe that, but often wonder about the dyno numbers themselves.
Boring a block should only be done to clean up the cylinder(s) for the new pistons. On a 318, an added bore of .030 only yields 4.9 cubic inch's. (318.2 to 323.1) That ain't nothin in a build.
Less boring of the engine is better for a stronger stiffer less flexing cylinder wall for more power due to best sealing. Not that going .100 over on a 318 will kill it. (*Well, maybe, sonic check it first!* ) But boring out an engine is equaling less life due to less rebuilds in the future.
If you need to, then fine, but, IMO, don't do it for 5 cubes, do it only because you need to do it. 5 cubes won't make a difference.