I do seem to remember a thread somewhere about modifying or making a hood but it may be over at www.photo.net in the archives.
I for sure don't remember what lens/hood combos that came up but the thread was fairly extensive so it may be worthwhile searching and weeding through the info.
Heck, there probably is some pertinent info on apug also.
I have the round style stock Hasselblad lenshood for the older 50mm "C" lens. I would say I could measure it for you but I doubt it would be of any help.
I was thinking you might be able to get the depth measurement off a pro shade but that wont work either because the outer dimensions would be different.
Good luck and I'd try searching for awhile both here and on photo.net if you haven't already.