Shotgun question
 

I have an old Mossberg 500 20GA shotgun that my dad got me when I was younger. I am working on setting it up as a tactical home defense shotgun. I found a tactical stock with pistol grip that will work, a decent heatshield (mainly to help blacken out the shotgun b/c its currently all camo), and a top weaver rail with a 4 reticle Reflex Sight. The problem I am having is finding a forend. I found one I like but it says that its only for the Mossberg 500 12GA. The only forends I can find for mine are tri-rails with very short rails. I want a single longer bottom rail to attach a forward pistol grip and a combination tac-light/laser sight directly in front of it for easy on/off w/out having to run a wired pressure switch.

Can anyone tell me the difference in the 12GA and 20GA forends? Is it something I can easily modify to work? If I have to, I can do a tri-rail, but I would much rather keep it clean and simple.

Thanks in advance.