But guys, if folders are out because the difficulty using grad filters, then Mamiya 7 isn't going to cut it either. Read the OP again.
Bronica GS-1? Maybe too heavy too? A small LF camera - like a Galvin with a 6x7 rollfilm holder and a 65 mm Angulon.
It's not actually the difficulty of using grads on a rangefinder (I use them easily enough on my Fuji GA645zi and Fotoman 617), more the shape of a folder - it looks like the Lee lens-mounted thread might be incompatible?