Congratulations, it's a nice long distance rider. Mine had a mustangseat and I put on 1700 miles with no monkey butt. You might have to replace the pivot shaft bushings if you feel the back end wiggle. Good luck with your new bike.
I remember my neighbor bought one of those new in 1980. Best i recall it was slower than christmas because of shovel motor in big heavy bike. The enclosed chain was a big pain also, kept seeping grease. I guess there was no way to fix that. I think he finally just removed the covers and ran an o ring chain and it worked fine.
An original '80 FLT can be an investment, providing it's in good shape. But it will take a while to redeem itself. If it's in good shape, I wouldn't mess with it. JMO