Whether any type of planes have tv screens in the headrest or not, is actually up to the individual airline itself.
Any type of airplane can be fitted with them, its whether the airline feels it worth the investment.
You would be better off calling the airline itself and asking the question or I'm sure there is someone on the boards here that will be able to answer your question specifically relating to Delta's MD-88's.
CDN Prince Charming
(Belle1627's DH)