The plans for the Dakota I'm building came with a sheet of four
alternate arrangement plans in addition to the one "streetcar style"
accommodation which was the basis for my choosing this plan. It is
similar to Idaho but 7 feet longer. The fact that so many options were
presented including just using the hull as a big skiff with no cabin at
all, indicates to me that you can play around with the cabins on these
designs quite a bit to suit your needs (within limits of weight and balance).
I built the cabin with headroom varying from 6'1" to 6'3". I might have
been able to get another inch or so out of the width of a 4' sheet of
cabin side material if that had been a requirement for me. If not, it
would have been fairly simple to splice a narrow strip at the top.
You can always sketch any modification you are contemplating and fax it
to PCB. If you are a paying customer, you will get prompt feedback.