I've transformed my Mossy 500 into my ideal HD tactical weapon. Pics below. Here's a list of things I've added:
Butler Creek steel folding stock - the steel is a little heavier than the composite folding stocks, but it is simple and easy to operate. More comfortable for me, and provides some balance when unfolded. Folds out of the way so you can use it either way. Comes with swivel anchor. I liked the way it mounted and the pistol grip fir my hand well and had a comfortable trigger distance. It's not adjustable, but it happened to be the length I needed.
Side Saddle 6 shot - mounted weak side for easy re-loads on the fly. It does not get in the way on the Mossy 500 stock fore end. Easy to install and does not require permanent modifications.
Sling - It came with swivels and anchors (one screw-in butt stock anchor and one mag tube cap with anchor. I just screwed the anchor into my stock mag tube cap. I did have to modify the sling to work for me. It was basically a shoulder sling. I took the screws out of the loop rivets and let the overlap out on each end and put them back it. This made it long enough for me to use as a tactical sling. It isn't adjustable on the fly, but this worked out great for the length I needed. It was also very inexpensive and came with everything I was searching for in one package.
Flashlight with strobe and remote pad - thanks to fellow member SigP250 for the recommendation of this light from Combat Optical. Simple, easy, and doesn't break the bank. Works GREAT. Comes with push button end cap to use as a regular flashlight and also a remote pressure pad end cap and mounting ring for tactical light. The strobe feature is AWESOME. Hold the pad down for regular light, let off and hold it down again for strobe. The mounting ring that comes with it isn't the greatest. I had to get a little creative with it to make it work, but the end result has some benefits. The ring is actually only around the end cap which moves the light forward enough that it doesn't get in the way of the fore end. It also makes it possible to unscrew the light from the pressure pad end cap and install the button end cap to use as a regular flashlight without having to unscrew any of the mounting hardware. I also bought a mag tube tac rail and mounted the light at 3 o'clock. I actually used black tape mount the pressure pad to the fore end once I found the right spot. We'll see how the tape holds up. This was a VERY affordable light and came with everything in one package.
All in all, it came out exactly how I was envisioning and is functional and versatile. Just thought I would share the project I've been working on and thank SigP250 for the light recommendation.