It actually is a heavily Sovereign-influenced Galaxy cross-breed. It exists in between Nemesis and Picard, if I remember correctly. So, 2385–2395–ish, I guess?! That would make two or three refits, if I remember correctly. Since the Ross is an NX-prototype, that will be its trait, in addition to “Federation Starship”, of course.
The Sovereign’s systems differ from the Galaxy only in one points in Engines and Computers, respectively. So, take the Systems of a Constitution Class. I’d say, add a point to Comms or Sensors to stress the multi-role-explorer build of the spaceframe. I go with Sensors, since it’s a science ship, afterall. If you want to stress the fact that the ship is very experimental (two warp cores!!), you could also go with Engines instead of Sensors, but that would make the ship a bit engines-heavy and also prevent any Refit-improvement by the rules as written.
Both ships add to Command and Science in their Departments stats, I would keep this. Since I went with “Sensors” under the Systems stats, I will now add the third point to Engineering. Because, well, you know, the ship has 100% more warp cores built-in than any other Starfleet ship I remember.
Both spaceframes have the same Scale.
Both attack with Phaser Arrays, Photon Torpedoes and a Tractor Beam of identical Strength, so I will obviously keep this, and add the more modern fourth attack of the Sovereign as a bonus.
For Talents, I will go with Saucer Separation (obviously) and Redundant Systems (did I mention the exceedingly high amount of warp cores on that ship?). I also add an EMH (model 3, perhaps?) and the talent for the fourth attack (see above). This leaves one talent-slot open for a free choice by the players.
The Ross itself is most likely a “Technological Test-bed” build, and since it has two warp cores, they most likely chose Improved Warp Drive for a talent. But you could say that it was built for Strategic and Diplomatic Operations (because there is that embassy and the promenade) and include the Improved Warp Drive either in the Spaceframe itself or make it a very reasonable player’s choice. In case you chose “Technological Test-Bed”, including “Diplomatic Suites” is a very, very reasonable choice.
So, this would be my Ross. I will provide full stats, if one of the Modiphius- Accounts permits.