I think you're talking about the valve bodies that thread into the distributor head on the driver's side of the pump. You may need to check the length on the bodies before you swap. They came in different lengths. In fact, you may HAVE to swap them.
Be careful when doing it. There are small pieces in there that can fall out. Inside the body itself is a shim. You definitely don't want to lose that.
If it were me, I'll pull the bodies off the ECO pump and see how they go together. Keep the pieces from each valve body together. Then, swap them.
I think they should flow the same, but the pop pressures might be different. Either way, if you replace one, replace them ALL (i.e. don't switch between pumps: switch all, or switch none).
Or, if you have a small file, recut the threads on the TD ones.