DB plan has received a domestic relations order assigning a portion of pension benefits to the ex-wife that was enter by the court in 1978. It clearly identifies the plan and does a pretty good job of specifying the amount assigned to the ex-wife. Insufficient for us to determine how and when to pay.

Myunderstanding (which I hope you will confirm or correct) is that a plan may treat a pre-REA order as a QDRO and pay benefits to the ex-wife (alternate payee). In this is correct, we plan to go back to the parties and tell them that the 1978 order doesn't provide the plan enough information to pay benefit, and then ask them to get an order that would constitute a QDRO.

This seems deceptively straightforward. Am I missing something?

Thanks.

Your approach seems inconsistent. The Administrator's duty, upon being served with a DRO, is to make a determination whether the DRO is a QDRO. If it is, the Plan will honor it. If it is not, the Plan will not honor it.
Administrators are given considerable discretion in being able to call DROs QDROs. This is because it's easier to honor such an order than to get mired in litigation, especially when it's not the Plan's money.
This is a long way of saying that your determination to require them to go back and obtain a clearer order is based upon a determination that the DRO is NOT and QDRO.

A pre-REA domestic relations order may be given effect as a QDRO. How and whether that is done depends on the circumstances.