If its just dirt and crap ruining the bearings, that doesn't really call for line boring, if the block is ruined another way somehow, it might be cheaper to find another one, or go to another machine shop, there should be no problem with checking the alignment before you go to the expense of boring it, and it shouldn't be a forgone conclusion that it needs it.
And before any 'experts" get wound up, I've been a machinist for over 35 years.
