It is a very feasible conversion and I am well into doing one. Some in-progress photos of where I am with it are attached:
I am building the Sumner as constructed, with the early British-style bridge which I have always liked the look of. The references cited by Ed Grune are the ones that I am using. Be aware that the Floating Drydock plan books do not contain full sets of plans. They show partial plans of each part of the ship, but do not contain a full sets of overall plans. You could probably print out the partial plans and paste them together to create an overall plan, but it is much easier to also buy a set of their USS Walke plans and then have them reduced to 1/144.
As others have stated the Fletcher and Sumner hulls were the some length and basic shape, but the Sumner was 14” wider. This works out to less than 1/10” in scale or 1/20” per side. You could probably add 1/20” wide strips of plastic to the deck edges, gradually taper them to nothing towards bow and stern and easily squeeze the deck into the hull, but I am not sure the small increase in width would be noticeable enough to make it worthwhile. The twin rudders are not hard to make and the shafts and propellers can be used as-is, although I believe that, at some point, Sumners and Gearings received four-bladed props.
The deck needs to be scraped and sanded clean, if you are careful you can cut or chisel off the deck hatches and reuse them. Almost everything above deck will need to be scratchbuilt. Major kit items that can be used are the funnels (with some minor modifications, depth charge racks and throwers, torpedo tubes and the gun director. I would recommend ordering 1/144 twin 40mm mounts from WEM. (They have mentioned that they might make quad mounts also, but combining two twin mounts to make a quad is a fairly easy job.) I have constructed the superstructure and gun houses using sheet plastic. The forms are basically rectangular and angular, and are pretty easy to fabricate. Due to the way the Revell kit is engineered you get six 5” guns, so I have used them in my scratchbuilt gun houses.
Unfortunately, 1/144 USN fittings are not plentiful. Two of the items you will need to make are shown below.
The kit provides the early style round ended life rafts and the Sumners, for the most part, were equipped with the later style rectangular type. The firehoses are molded onto the Revell kit superstructure parts. They are molded too shallow to be cut off and used and there are not enough of them anyway. I am making my own by wrapping very thin strips of plastic around a form, lightly gluing them together with liquid cement, and then cutting off the ends of the loops. These will be hung from scratchbuilt brackets with valves and nozzles to be added. The Floating Drydock planbook is full of details that can be added to the kit.
Hope this helps. Good luck with your build if you decide to attempt it.