Can't comment on your specific question Neil, but I can't help but think this is not a great idea with a Hasselblad. Getting a bit closer, maybe for a tight head-shot or something, is one thing. Proper macro, if that's what you're thinking, is quite another. You would need long tubes to get seriously close with that lens, and I don't know how coupling with the in-lens shutter would work, or how image quality would hold up. Lots of practical problems. Macro is not Hasselblad's forte.
You have a Nikon...