Ah got ya thank you !
MODIFYING THE MAGPUL SGA STOCK ON A 590
I had seen this from two other posters, but I can't find their pics, so here is mine.
Limbsaver does not yet make a recoil pad to interface directly with the Magpul SGA Stock for the 590. However, there is a backdoor way into putting one on. In addition to the Limbsaver part (10101), you purchase a MagPul 870 OEM Butt-pad adapter ($11 bucks at Amazon). This adapter plus the Limbsaver interfaces perfectly with the Magpul SGA Stock.
My pic below shows my final stock setup (plus I show the original Magpul SGA butt-pad adapter above it). LOP = 13.5" (with two of the Magpul spacers) which I think is about optimum for most people. This is the middle setting, so you can add 1 or 2 more spacers or remove 1 or 2 based on your build and preference.
While the original Magpul recoil pad is much softer than the OEM Mossberg pad, the Limbsaver is softer still. I also like the way this pad fits my upper arm/shoulder compared to before.
IMO, this is a sweet setup.