The bridge house on a '64 Maddox is enlarged and enclosed, perhaps the largest change. Change the pole mast to a tripod mast and change out the radar suite.
Add ESM antennas to the aft stack. Change the radar on the MK37 to a MK25 dish.
Navsource.org has some decent photos
You mention the armament, so you are aware of the 3"/70 replacements for the 40mm BOFORS. Tubs will need to be adjusted for each of these mounts. They are a bit larger than the 40 mm mounts. There is a director structure for the aft twin 3"/70 that you will need to add.
Loose all the 20mm guns and gun galleries.
As lost, the Abele had a quint torpedo bank between the stacks. Loose that.
The Maddox had just one depth charge track on the starboard side. Loose the port one.
And you may also be aware - re-print all of the kit hull pieced which are done in camouflage into Haze Gray, with a large shaded hull number.