Scanned document is a preseries MiG-1 flight test report and the photo shows I-200 seat. Text above the photo says that tested plane didn't have shoulder straps and that the straps "will be installed", presumably on series machines. Were they really installed on series MiG-3s, nobody knows...
Regards,
KL
PS. This was posted while I was typing:
Hi Massimo. This handbook said "
no shoulder straps for now but maybe fitted latter" I am a Russian and if Russian telling you "not for now but maybe I'll do it latter" that means (99%) - never
Strictly speaking
it doesn't say "for now" and it doesn't say "maybe"!!!
It only describes then current situation - "shoulder straps are absent" and what will be done in near future - "they will be installed later on"