New here and just found your thread,if you are still looking for a solution I'd like to share a remedy use by a place I worked some time back.
We needed an 11x14 sized copy camera to replace the 8x10 we were currently using.Utilizing an 11x14 back we already had, we added a box to the rear of the 8x10 about 10" deep and a little over 11x14 to accept the larger back. The copy camera didn't need back corrections and I'm pretty sure your portrait camera won't either, it looked a little strange but we used it for years.It was an inexpensive answer to our problem and made my boss happy....