Last chance 1946--- You may find that the rideing position on the FJR actually helps your back. I to have been rideing for about 45 years and have lower back problems. When my back is hurting (as long as its not really bad) I can go for a ride and it actually seems to help somewhat. My 03 is the first sporty bike I've owned and I love it, I'm sure I'd have a hard time going back to a cruiser. You may find yourself wondering why you didn't make the switch years ago.
By the way, I sure hope this isn't the last bike I'm going to enjoy because I feel like I've still got lots of miles left in me! Just getting broken-in 44