Dear IRG.
Please consider Brigade Firearms Makasi AR/FAL hybrid
Discussion and videos - https://www.canadiangunnutz.com/forum/showthread.php/2404896-Brigade-Firearms-Makasi-AR-FAL-hybrid!!!/
Consider you can work with manufacturer and use it with your NR lower:
Or consider submitting to lab.
Or both ways at the same time.
Please consider Brigade Firearms Makasi AR/FAL hybrid

Discussion and videos - https://www.canadiangunnutz.com/forum/showthread.php/2404896-Brigade-Firearms-Makasi-AR-FAL-hybrid!!!/
Consider you can work with manufacturer and use it with your NR lower:
That kind of upper can be easily redesigned at the rear end with a push pin.
They all use AR FC this means they all have the same firing pin height for the AR hammer to swing onto. This alos means the distance between the hammer and the breech are pretty much the same if you think about the relationship amongst all the guts.
The easiest thing is to ask IRG to resurrect their NR18 lower which has a FRT already, and slap a modified version of this upper on top
Or consider submitting to lab.
Or both ways at the same time.