Lower receiver dimensions?
I'm not sure what you mean, but the lower receiver is slightly larger than standard forged lowers, due to the material used.
It will take some aftermarket parts, such as Norgon Ambi-catch, and most pistol grips. However, ambi safeties will generally not fit, and there may be some issues adding Magpul pistol grips, not due to fit, but because of some internal issues with voids in the mould.
There are also fitting issues with other items such as BAD levers, and of course, it will not fit with a standard AR upper.
Regards.
Mark