Looking at the labels on CDMS, I see there is Me-Too-Achlor and Me-Too-achlor II. The first one does not have the safener in it, and is NOT labeled for corn.  The "II" version does have the safener in it, and is approved for corn. So, if you have the "II" version, you have the one with the safener in it.

On the "II" version's label, it says you can apply Me-Too-Achlor II alone on corn up to 40" tall for post-emergence of lay-by.

If you are applying glyphosate + Me-Too-Achlor II + atrazine, you can apply on corn up to 12" tall.

If you are applying Me-Too-Achlor II + atrazine, you can apply on corn up to 5" tall. 

So, I would say the Me-Too-achlor II is pretty safe on corn post-emergence. The reason for the 5" restriction on Me-Too-Achlor II + atrazine is more due to controlling weeds, rather than crop safety.  Once weeds break thru, the Me-Too-Achlor II + atrazine is most likely not going to control them.  Adding the glyphosate - as you suggested - will be the key.

I will add that the later you wait to spray, the later into the season the Me-Too-Achlor will hold up.  I think that would be a good thing.