I've never seen the underside of an H-series engine, I wasn't sure how much material made up the caps (or girdle in this case) that you could afford to take that much away without compromising strength. If the '97+ blocks are done that way, I'd imagine the earlier units can also be done the same way. I also wasn't sure if you could machine away and then replace the bearing surface on a set of main caps or not. I guess you could use custom bearings or '97+ one's.

From what I heard, boring is the process of taking larger pieces of material away and honing is a finishing cut (so to speak) that only removes a small amount of material but leaves a nice finished surface.

I'd assume that a machine shop would have some way of locating the block so that whatever machine they use to cut or mill the material away stays dead center. I work in a small tool and die shop and we have vices built into milling machines that you can zero out and work right dead center of whatever material you were using. You could never fit and engine block in one but the theory is probably the same with a larger custom built machine. Let us know what you find out, I'm interested to see if it would work.