HB, the belly is radius somewhat. mainly the corners are rounded to give it some flow and help with tweaking the tiller.
this bow came from a very straight stave which I cut myself. I haven't worked with this wood much ,so I am not real sure what one can and can't get away with, although I do feel that one has to give it some width.
I haven't tried a longbow from it.
Thanks for the good words, and good luck with yours.