Looking at that spec sheet, I really don't think there is any difference at all.
The fact that the 1000Base LX module says it works on multimode is irrelevant - all single-mode optics will work on multimode, however with significant loss (hence why the distance is reduced from 10km down to 550m on multi-mode).
To answer your quesiton though, yes - they are both rated to 10km on single-mode fibre.
Just remember though that distances are quite meaningless when it comes to actual real-world performance. If you have poor quality fibre with lots of splices in it, then an optic may not be capable of achieving good signal to 10km. Always measure the path loss, and use the minimum launch - receiver sensitivity to work out which optic is right for you.
This page:
http://www.juniper.net/techpubs/en_US/release-independent/junos/topics/reference/general/pic-m120-gigabit-ethernet-iq2-sfp.html
seems to suggest that either of those optics will work (I've not yet seen an optic that won't work in an M-Series)
Hope this helps