Had a long but successful day - as promised i'm gonna upload nut size dimensions for future reference, thing is i'm not sure this nut is OEM it measures 40.8mm..i have removed it with technique showed in youtube video posted by @Iahawk (thanks!!).
Whole procedure was easy and fun i suggest everyone who has time and tools to try it out - results are great, drove it in only in garage though - it was raining outside.
But i can feel the revs going up and engine not bogging, everything was serviced, greased, sanded, torqued to specs.. all parts were in pristine condition (lucky me buying it used with 48000km, with no knowledge of motorcycles mechanics etc .. ) only thing i have changed is not OEM rollers (my guess RMS by the looks) weighing 15.5gr to RMS 13.43gr rollers ..