Nikos,

.. PeterP have a point ...

I am using the YS160 with the 821 muffler, hyde 140ARA mount ( seperate nose-ring, alu-beams) servos in tail (3421sa) and the Li-Ion mounted far aft , and my CG is 180-185 cm ...
If you put additional OZ in the nose, it will be more likely you need weight in the tail ... at least when you want to play with the CG ..

The stock ring are fine, light and strong ..

Kjell Olav