No. Seats can be selected in advance for Value-Economy fare group and up (that's Y B M U K H L, below them are Q T E N R) and if you're an elite. Call and ask anyway.
Preferred seats of that one row in economy (you mean Space+ seats, right?) can be selected only at the airport check-in counter. For you it should be free since you are elite plus, but then again, you might have troubles with recognizing delta status.