A replacement back seems to be in the possibilities, but with an extension back I guess that a lot of stability issues will come up. The back will be located too far from the tripod connection and the camera will tend to flip over.
I'm thinking about that for my 8x10 C-1, which is a very heavy and stable metal camera. It allows the camera to be slid along the rails to center it over the tripod. I was thinking about 11x14, which would not require much extension. I don't know if 7x17 or 10x20 would work out.
juan
From looking at various formats of Korona that appear to have same rail version, I would think a back & bellows could be readily adapted to field cameras with rail tracking. Only requirement would be ease of attaching bellows to front standard.