okay i got some time to pull apart the 2004fjr1300 final drive that i recently bought for $20
they only difference i can see is the shaft is longer on the fjr
and the fjr housing does have the shock mount drilled.
they have the same number of teeth pinion and ring gear 33/9
they have the same hub to wheel spline in both and the same offset.
here are some pictures of my old final drive that blew up and the fjr one.