I don't think it's crab apple, at least the species that I have seen before. The fruit is a lot smaller than I have seen on those unless it's because of the location of the trees, it was sort of a bottom lands type area. Lots of water, reeds and such. Most of the fruit on the trees looked to be smaller than most grapes, those bunches you see are about three inches across if that.
Any ideas on how long to let it season at bow size? Does plum usually dry in a few months if you get it down like most other woods?