Can the Marine model be fitted with the same heavier springs and extractor as the Police Magnum? The Police is the one I want for the HD job but I have wanted the Nickle Marine from the first time I saw one so I am hoping to blend the two into a perfect HD for me. Would also PROBOBLY be going with the topfolding buttstock and a tac light up front.
Is there some other problem with this idea that I might be missing?
I had a 16ga Wingmaster many years ago but sold it as the shell supply began to dwindle, had problems getting #2 or #4 for turkey season ( this was before the internet and online sales ) and just moved on. Been concentrating on SURs the past few years and an HD 870 will fit right in.

The extra-strong springs on the Police model are:
The magazine spring.
The shell lifter "carrier dog" spring.
The Trigger/sear spring.

Note that the extra strong magazine spring is used ONLY on the 4 shot standard length magazines.
Remington uses the same springs in guns equipped with a magazine extension, so you won't need to buy a different magazine spring for a Magnum Marine.

I'd suggest not installing the trigger/sear spring, since this was intended to make the trigger pull a little heaver to prevent accidents.
Contrary to popular belief, Remington doesn't use stronger shell releases in the Police guns.

The Police and Wingmaster use a milled extractor.

The Police does use a compressed powdered aluminum trigger plate, but the plastic Express plate you get on the Magnum Marine is just as durable, has no finish to wear off, and will bend, flex, and return to shape if bumped where the aluminum will stay bent or break.

So, about all you need to do to upgrade as much as possible to the Police model is to install the carrier dog spring.

Current 870's are coming from the factory WITHOUT the locking safety button, so try to make sure you get a new, current model, or you'll have to replace the safety.

Thank you all for responding, I have just closed a deal on a Marine Magnum so I'll be looking at the milled extractor and the carrier spring. Looks like I will have a great leadslinger on my hands in a week or so.
Mike I read that article a few days ago and it is what pressed me to look into the Police Magnum rather than the Express. It's a great thread and deserves it's tack status.

I've been carrying a marine magnum as my duty shotgun for about 8 years now.  I ahven't done anything except for surefire forend, side saddle shell holder, and stock/sling.