Offset grinding 460 cranks from the 2.500 Ford rod journal to the 2.200 chebby journal is common practice, albeit less so since the chinese stroker cranks have flooded the market. Personally, I still have a preference toward the factory offset ground cranks over the chinese cast stroker cranks. These days, it usually costs more offset stroke an oem crank than it does to simply buy a mass produced chinese stroker crank (maybe not the case down under?) but I like getting my crankshafts set up exactly as I want them. Also, you have a few more stroke options this way.
Generally speaking, when offset grinding a factory 460 crank to a chebby 2.200 journal, max is about 4.14" stroke (4.15" if you grind to BBC .010" undersize, etc.). People have successfully gone to a 2.100" journal and made a 4.25" stroke, but I don't recommend this.
When working with the factory componentry, it's important to scrutinze and select your parts wisely and go from there, because all oem parts are slightly different (loose manufacturing tolerances due to passenger car applications). I know of 4.14" stroker 460 cranks that have supported 800+ HP and others that have managed 1000HP. But hey, some may not handle such abuse (the key word here is "abuse").
A lot of things are to be considered when reducing journal size and changing the stroke of a crank, such as where the rod journal's oiling holes will be when finished, how the lightening hole in the crank throw may restrict the desired stroke capbalities of the crank, etc.
To view engineering drawings of several possibilities of oem offset stroking click here
and select "Crankshaft Journal Overlap Drawings."