160,000 miles will not get you 2 BusClass seats...
If you are lucky and flexible...you may get 2 Coach Award seats...
at 80,000 miles each roundtrip to SGN.

The M Class fare from MSP to SGN on DL and KE codeshare
is over $3,200. EACH for two weeks in mid October...
way too much to even consider IMHO...then
using mileage 50,000 miles each ticket...to upgrade to Business.

Call Delta and ask about KE - Korean Air...
from one of its cities it flies from in USA...
just maybe you can get there in coach using DL
and/or partner airlines...such as Korean Air.

Also, look at flying into other Asian cities which have cheap flights
to and from SGN...such as BKK...for example...
Air France has cheap flights daily fm BKK-SGN.

Good Luck!
tj