Thanks! What do you mean use factory body mounts and bolts? Will that only work if the cage lines up with them? I bought a prefab family cage from JBG that comes pre-welded. Do have any photos you can share?
If you have floor bars, you can run them so that they are close to the body mounts, you then add a plate to the floor bar, and then bolt the floor bar plate to the body mount. It is about a safe as you can get when it comes to cages. Because you have the added strength of the floor bars, but you also have the cage firmly attached to the frame so it's going to take a whole lot of force to eject it. Floor bars distribute the compressive force across the entire length of the bar and compress against the frame rail in the event of a roll over, you therefore take some load off of the rest of the cage by distributing that load laterally across the truck and onto both frame rails. Instead of focusing the force on a few tie in points, that being said just tied to the frame is very strong and if that is what you have, you should feel very confident in it's ability to protect you.