The tang safety is possible and I've done them in the past as a special order. The tang safety was never considered for this rifle build.
In regards to the rotary systems, I've used the Recnagle G9 plus on my rifles. It's a good system. Repeatability is decent, 1 MOA near as I can tell. Being a true one handed release system is nice. It keeps the rifle clean, free of levers and so on. From a cost perspective it's 2/3's the cost of the claw mount. The G9 rotary gets along better with large diameter objective lenses as well, which for the most part can turn into a fitting PITA with the claw mount.