Only one thing. Your forearm might need to be replaced with a separate forearm action tube. It's a metal tube that fits down over the mag tube and the forearm slides down over it and is held by a nut at the front end.
Maverick 88's are sold with a one piece forearm that has no separate forearm action tube....the action bars are riveted directly to the plastic of the (usually ribbed) forearm. To use aftermarket forearms, and your wood would count as an aftermarket one if you have a one piece, you have to replace the one piece forearm with a separate Mossy 500 forearm action tube. That metal tube will allow you to use a wood forearm.
Why did I say that? Well, Mossberg realizes that most of its customers use the synthetic these days anyway, so they've been putting the Maverick 88 synthetic, one piece forearm onto the Mossy 500A's tacticals (HD and Persuader etc) for the past year or so.
Slide your bolt about halfway back and remove your barrel and see if your forearm has the two notches at the front to unscrew the forearm action tube nut. If it does, unscrew it and pull the forearm off forward and you'll see this part. The nut is at the right end.
http://pics.gunbroker.com/GB/123668000/123668002/pix254298671.jpg
If your forearm *doesn't* have that slide tube, that's the part you'll need to buy. It usually runs in the $25 range so don't go overboard on one.
If you need anything else....
richard