So do you want the pull out system, or do you want the cradle system? Or do you want a pull out system that uses the cradle system?
I don't see how the cradle system would save you much, if any room, over just the standard set up in the safe.
If you're a bit handy, I would say that pullout system wouldn't be hard to build at all. A small platform for the drawer slides, some nice plywood or solid board, and a little time with the skilsaw/router. The hardest part would be the drawer slides, but that isn't too bad, you'd also have to make sure to get a nice heavy duty set.
ETA: I missed the part about the SBRs/Pistol. It looks like the shelves have built in standards, so it wouldn't be hard at all just to add a another loop, or even just a single sided loop for the shorter rifles. They might also fit with the stock extended all the way, that's what I have to do with mine.