Humbrol 164 is equivelant to Model Master 1723 / 4752 Gunship Grey
Humbrol 163 is equivelant to Model Master 1710 / 4726 Dark Green (FS 34079)
My go-to conversion chart is here:
www.paint4models.com
Simply check to the both paint brands and you will see them. However, it comes down to a science because sometimes a certain color will be the same as a different shade. Choose what you think is the best match and go from there.
Better yet, enter the FS number in the search area. You'll have better luck this way as well.