I did some more work on the bike (read: disassemble it completely) and checked the components. The fork states '90 on the tube (but it could also be stock). Both the FD and the RD state '90 too so my best guess is 1990 stock and assembling 1991? I can't really find the right words but the bike does feel way more 90s than 80s. It's light, the looks, etc etc. Funny thing about this dating stuff is you wont ride any faster by the knowledge but I always want to know everything of my hardware

edit: the BB cup states nov 1990 so good guess i think