Sounds very similar to the setup on my road bike, a very old Sora front triple shifter, newer 105 front mech and a MTB triple crankset.
I've found I can get it to work, with fiddling, but
- more spacers on the NDS than DS, for chainline.
- cable outers longer than you'd think
- fiddling with the limit screws
not perfect, but when road triples are getting harder to find, you take your choice