Hmmm, didn't know there was a tie rods difference with different diameter rims? Just saw on RA there is a 18" option for Motorcraft.
https://www.rockauto.com/en/catalog/ford,2012,mustang,5.0l+v8,1501235,steering,tie+rod+end,7428
Does your car have EPAS?
I always do both sides and even...