1977 cr125 assembly question

Hello, I have a 1977 125gp that I a reassembling, my manual for the earlier 125s 6 speed says to align the drum to 4th gear. On the earlier bikes this is easy to locate as it uses a detent into a particular position in the drum. On this bike there is no detent, it had a mechanism on top of the shifter drum. Can anyone tell me how to align the drm to 4th gear?

I managed to find this thread and the right info in the manuals on this site, thanks

http://www.cafehusky.com/threads/need-help-with-transmission-1978-125-cr.87527/