I looked into this for my '03LR. The FXDX came with dual front disks. If you can find all the parts, that is a way to go. Otherwise it gets 'expensive'. You can stay with the single-disk and there are 4-piston and 6-piston calipers that work with the OEM disk. I ended-up changing pads to Lyndall Gold and left it at that.
Veteran/Retired IBEW Lu520
2003 FXDL Stg 1 AC, SE slipons
CVP Tuner carb kit
Andrews Hyd kit w/21n cams
Ohins shocks, Intiminators in forks.
Mustang Vintage Solo & Pass seat
J&S Dyna lift