Ok can 100% confirm 735XT has undocumented feature of turn by turn directions using just a course from GC. Fenix 3 tested side by side using same process does not.
I cannot see how you can edit the notifications in any way but it just works when you navigate a course.
Like this watch a lot already
Good to know does not only work for me then!
So how did you transfer the course to your units in the end?
What you could try is copying the course FIT file from the 735 onto your Fenix 3 - put into NEWFILES folder.
The fact that I could "see" the course points in GTC suggests that they are written into the FIT file and not auto magically created on the fly by the device each time you use that course.
... turn by turn directions using just a course from GC...