You use an oversized o.d. guide and offset bore the guide hole in the head with a boring head in a Bridgeport or similar mill... keep in mind that the seat will also need to be replaced and the port will more than likely need to be welded on atleast one side if not all the way around on the seat ring. I have done this sort of thing on DRCE and wedge heads for competition eliminator before. It can end up being a fairly costly and labor intensive project and thats why I have probably only done it on max effort type projects!
Have seen this done on wedge type heads without too many issues. However as previously noted you can expect geometry problems with the canted valves.
Dan pretty much hit the nail on the head moving the valve .030" to .040" is probably going to involve some welding and will more than likely get pretty expensive. I would only consider doing this for an all out competition application.
We moved the intake on one of our racing heads and the valve was re-angled from the rocker contact point. And @ .017 per inch per degree it was one half degree change that moved the 4.5" long valve .040..
Full race Mini engines used to do this in the 60's. They would offset the exhaust valve by an amount that allowed you to cut a new seat that overlapped the stock seat, but larger than otherwise as you kept the side nearest the intake valve in the same location. I don't think they do it anymore.