I believe the deckheight of the 2v block makes the compression too high for the 4v heads without some kind of work like shaving the heads or something.. I don't know exactly, perhaps someone with better knowledge will chime in.
You can do it but it's alot of work and will be rather pricey. Do a search as there have been alot of threads started asking that very same question. Like this one for instance: http://forums.stangnet.com/showthread.php?t=669470