I just bought a Mossberg 500a with the 20" barrel and pistol grip. I want to take the pistol grip off so that I can actually shoot it accurately should the need arise. But...I'm having a hard time finding a non-tactical, plain buttstock for the 500a, even Mossberg couldn't help. My question--there are plenty of Remington 870 buttstocks around. Will this fit the 500a?