The reason that I do no have this viewing set is no brain teaser, this Flexbody, etc, was a gift from a friend and I do no question his very generous gift, period.
I am more than happy to continue using it as is, with the ground glass, and get the viewing filters as I can, which is why I posted in the first place.
The Hasselblad chimney view finder will work with the camera, and I'll get one at some point, and, the ground glass is just fine with a long loup, as with a 4" x 5" or larger camera, though I hope to trade up at some point for a better quality one than I have now
The Waist Level finder also works, particularly if you have a seated p.o.v. for composure and shooting.
I like the Flexbody, even if others find it fiddly and I won't let the lack of the filters deter me from using it.
I can shoot Instax Square film to double check shoots as needed, if I have any doubts and I expect quality backs using this film to be shortly forthcoming go Hasselblad analogs.
Cheers