I have used the CFV-39 on my 903SWC and it works to satisfaction. There is a little magenta cast which can easily be removed with Phocus or with CS5. There is no blur in the corners if I work with f>8.
The CFV-39 is 1.1x crop. The H4D-31/40 is 1.3x, which was the subject of our off-line conversation. Sorry, if that wasn't clear.
What I find confusing with crop factors, is the acceptance of the Hasselblad user base to accept the 1.5x crop on the vertical dimension. it's taken for granted that (6x4.5) is all thats available, so accept it ..... etc.
Now, I've not met, nor read about, a single Hasselblad user who thinks a Mamiya/Pentax 645 is the same tool as a 6x6 V on film. Never met a Hasselblad user who used the available 645 back as the preferred back and in fact have never met one who actually owned a 645 film back. But we seem to shrug our shoulders and accept that the wide dimension, defines the crop.
Well, purchase a 645 V back, put it on your SWC, and tell me if it works for you. I suspect you'll notice something missing.
I also read that the CFV-39 is not suitable for the SWC, but I don't know if that's completely unsuitable, or only on the outer edges of the frame. Perhaps someone can advise ?
I've owned a CFV-16 and found the 1.5x crop too restrictive and sold it on. Despite what I've written above, I'm really interested in a 1.1x H4D for the AF feature, but the price of that baby is well outside my budget and so, I'm contemplating a used CFV-39 again and hoping that the extra pixels, vs the CFV-16, will make up for the 50% vertical crop for portraits. I hope somebody here will expand on that.
Maybe, I'm not giving due credit to the H4D-41 with it's heavier crop and missing the advantages of the camera compared to the CFV option.