Two questions: Are you going to need an offset front sprocket? If so you don't want to be swaping them about because they cost about 4 times as much as a normal one, so decide that first and mess about with the rears as you need.
Second, are you running an extended swing arm? Because if you are, this could cause the chain to fowl the swing arm. I have an EFE engine in a GS750 frame and had to go up to a 17t on the front to clear the swing arm at the pivot. The longer the swing arm, the more likely it is to eat through your JMC arm. Too big a rear sprocket might cause a problem with the ch