Re: identify gearbox
A standard UN1 has high risk to break above 40 mkg of torque. This considering the Yield trength curve of the steel used and the different shaft sections. Obviously this value may vary according to the resistance the car offers to the force moment (weight, tyres friction, air resistance with speed etc...) and also by the heat inside the gearbox. Anyway keep this number (40) as a pivot for a standard use of the gearbox. Below 35 it is ok, 35-42 is the high limit, above you need upgrades.
A NG gearbox is the poor sister of the UN1, weak gearbox even if at first glance it loks like a UN1, it is really weak and clearly not safe for the use you plan to do.
So better to sell it and buy a real UN1/UN5 if you want to go with Reault or any other brand according to the recommendations made here