The USS Nelson is listed as a Saladin Class destroyer launched in 2223 and as being used as a test bed for a possible frigate. The pciture with the twin engines is diffent from what I saw only in the registry number, which should still be NCC 546.
Other Saladin Class destroyers were used as test beds such as the NCC 506 Pompey, NCC 501 Jenghis, USS Hamilcar, etc. The Nelson was just such an example.
Aparently Star Fleet decided that the project was not so smart, due to the obvious lack of hangar space, and developed the Surya Class frigates instead.
The Nelson was rebuilt to Jenghis Class specifivcations in 2275 along with the other test bed destroyers, such as the NCC 506 Pompey.
The Belmont is interesting as it would have better endurance range, as a TOS period light cruiser than the Hunt Class (CL 1353 - 1369) or Kearsrge Class (1500 - 1549).
Other advantages would be in maneuverability over the Constitution Class cruisers.
I just think that these ships prove that not all TOS ships are modular or simple in construction.
I had a go at what a probable Belmont might look like in the TMP period. The small secondary hull concept looks good on a ship.
There should be an image of a Hunt Class somewhere on line. The one I found didn't make it that easy to see the details of the deflector mount drum as it was a port side view only. Fortunately, I'd seen the design many years ago from all angles and know that it is a small drum under the neck pylon. The neck pylon and defelctor was removed in 2245 so that an aft under saucer AWALT torpedo launcher could be fitted, to upgrade the class into light strike cruisers.
I haven't found any images or designs of a TMP version of the Hunt Class but it would probally retain the aft torpedo capability.
TOS period Hunt Class have ingle split aft phaser mounts the same as for the Ptolomey Class Transport tugs, which are derived from them.
I've noticed that a few of Jackill's designs are TMP upgrades of ol TOS based ships, and well done as well.
So, model please, a possible wish list......
Belmont Class (TOS and/or TMP)
Hunt Class in MK.I. pre-TOS mitt die tall bridge, maybe a Mk.II. TOS-period and a Mk.III. TMP period.