DTDK, I hate to say it but you are on new territory using the FLD triple tree. It might just be a Dyna ready version of the FL Softail or it might not. A LOT of people will be interested in what you find. Also, do you have a cost on the FLD trees yet?
Slick. any 16 inch FLH or FLS will work, just make sure it is new enough to have chrome spokes because that is most likely what you will wind up with in the back. I had to relace mine because it had really poopy looking stainless spokes. If the wheel comes with bearings, 2008 and newer are 25mm, 2006 & 07 are 1 inch. Both the 1 inch and 25 mm FLH front axle will fit your forks. Older than that most likely will have 3/4 inch bearings and those won't work.