It has been several years sence I have flown on Delta, but in general Delta has fine service, likewise Delta 727's are great airplanes, they do have a few years behind them, but from what I here those planes go can go and go, just keep on ticking. You can sit nearly anywhere in the cabin and there is equal comfort. The last time I flew on a Delta 727, the seats were red and blue mixed I believe. The MD-88 is also a fine plane, probably one of my favorites for that bird can really git up and go, sometimes you even pull a few "g" forces when takeoff power is applied. So, relax, Delta will serve you fine and you can feel confident that your travel experience will be an enjoyable one.
Have a great trip.