Have to say I can't ID what you are referring to?
Fuel rail is metal, lower intake is metal, O-ring at each end of injector seals it between the two metal parts.
Is there a bushing or other removable part in the fuel rail?
I haven't run across that before.
It would be a dealer part as far as I can say.
Good read here on changing 4.0l injectors: How To: 4.0 OHV Injector O-Rings - Ford Explorer and Ranger Forums "Serious Explorations"®
One other thing, the electrical connectors for the injectors are known to have the tabs break off, they get hard over the years and just snap off.
So have some small zip ties or similar to hold broken connectors to injectors, or get new connectors as needed; loose connector WILL cause misfires
I did find this diagram of fuel rail and injectors: http://ww2.justanswer.com/uploads/Ov..._fuel_rail.gif
Seems to list all the parts