For a non standard receiver, I think the safest way is to clamp between two strips of nylon cutting board. That said, I use a reaction rod almost exclusively, and it's never given me any problems. Unless the barrel nut is way overtorqued I think they're pretty safe.I'd be willing to be present for a build class and help with the do's and more importantly the don'ts. I can bring my tools. I recommend the clamshell upper receiver vise WITH the insert, I'm not a fan of the tool that fits in the barrel extension. It will only work with mil-spec uppers, it won't work with a lot of the high end uppers. I've never needed a lower vise block. You can make a front takedown pin detent tool, I can bring mine. As for the AR-10 platform, there is no "mil-spec" and dimensions and tolerances differ greatly within and between manufacturers. For instance- Armalite makes one lower that takes Magpul mags and another one that doesn't.