Looking at the picture, it seems to me that the shaft is way too short. The M900 shaft in my old 888 swingarm sat flush with the end of the swingarm - still couldn't get the clips on but it was at least the full length. I know the M600 swingarm pivot is quite a bit shorter (10-15mm IIRC) and so would sit back inside the swingarm, something that wouldn't help with the load/cracking issue.
The tabs on the frame are, I think on all frames (my frame originated in an M600 and has them). I have an Ohlins shock and originally mounted the reservoir on the side of the frame as per the supplied mounting rubbers but never liked it there so I made a bracket to fit it under the rear as per S models, simply a cut/bent piece of stainless steel sheet and simple enough to make unless you have a genuine one.
Where it was;
Where it is;
I'm sure you'd agree, much neater.
BTW, when you get to fitting the swingarm, if you need the plastic end caps and clips, I have a small stash as when my swingarm pivot slid out I lost one of the caps and could only source them in a pack of 10, similarly the snap rings.