I'm going to move this to the gunsmithing section Gunslinger. To strip off that Remington epoxy finish you need a stripper rated for epoxy. Brownell's sells a good one and also has some nice finishing kits for that oil type finish your looking for.

 

Brownells also carries the spanner to remove the forend nut from the slide tube.
If you don't know how to remove the forend from the shotgun, pull the slide to the rear and leave it there, remove the magazine cap and barrel. Then slide the forend forward, holding the receiver upright press the Left cartridge stop in against the receiver wall and slowly slide the forend forward. The bolt and bolt slide set loosely on top of the action bars so don't let them fall off.
You can also remove the wood from the action tube without taking the forend assembly off the shotgun but you run the risk of tweeking the action bars if the spanner nut is seized or overly tight.

 

Thanks Bob & asphalt cowboy!

I didn't know if the finish on the wood was polyurethane or something else. The finish has some light scratches, and it's pealing off in spots around those scratches. You can actually peal it off in little strips. There are a few small dings in the wood, but I think I can steam those out.

The magazine cap and barrel come off easily. I thought there was something (i.e. the cartridge stop) that you had to press in, but I wasn't sure about the action bars either. I knew you guys would have the answer.

Thanks again.

 

I think you can download or view the 870 manual online at the remington website, there are some parts you have to press to slide the forearm off, it may be eaiser just to unscrew the retainer nut from the front of the slide. I used a piece of flat steel to do it, I think it was 1/8 x 1 1/4 or 1 1/2