So I've decided to purchase a 12 gauge shotgun, The infamous Mossberg 500. Mainly for HD and also recreational reasons. I want to purchase the standard 18.5" and upgrade the following: Top Folding Stock, Heat Shield, Rubber Pistol Grip Cover, 6 Shot Side Saddle and possibly a muzzle breaker. I have found one used for $250.00 (I'm sure I can bring it down at least $30). I also have found a possible deal on a brand new 20" mossberg 500a for $275. IMO the 20" looks way better w/ the longer magazine (7+1) but would be hard to maneuver around my house in a situation. What do you guys think? Are these even good prices? What should I do? My other questions: Can you make the magazine tube on the 18.5" models longer? So they're aligned? Which do you think is the best for my HD shotgun: ATI Top folding stock, Choate top folding stock, Knoxx SpecOps folding stock? My 1st choice would have been the ATI Top folding only because it looked badass.. sort of like a spas-12. After a bit reading... my perspective has some what changed. Also, are 1 point slings compatible with any of the above foldable stocks? I tried googling images, but could not find any. Lastly, what is the difference between a Mossberg 500 vs 500a? Someone told me they were exactly the same? I would appreciate it very much if anyone with shotgun knowledge help answer some of my questions. The sooner I figure this all out the sooner I will be able to start placing orders.Thank you in advance!