"As far as I know" (note the qualifier, because I haven't see a factory-fresh MM recently):
The Magnum Marine is basically just the Express Synthetic 18", exactly like the model 25077, except the MM has a satin nickel plated finish.
These are "mirror images", one model satin nickel, the other with the bead blasted blue finish.
All the "special" parts for the MM are simply nickel plated, thus the special factory numbers.
This means that like all the Express models, the trigger plate is plastic, and unless Remington has discontinued it as reported, it'll have the locking safety.
Where I stand on this is, unless you have a real need for the anti-corrosion feature of the satin Nickel Magnum Marine, and can live with the bright finish, I'd either save the money and buy the 25077, OR I'd buy the top-of-the-line Police model.
Not to be advertising for anyone, but we now have an available source for real discount pricing on genuine Remington Police guns.
In some cases, this sources Police gun prices are very near Magnum Marine pricing, or possible even LESS depending on where you buy the MM.
The source is more or less selling Police guns as a hobby, and prices can be astoundingly good.
Remington Police Guns.
Kevin Wells
Discreet Ordnance
kevin.wells@disc-ord.com
A number of buyers on other forums have done business with Kevin and report fast, very good no-problem service, and prices too good to pass up.