Compression fittings are available in both brass and steel. That one looks like steel. Steel will hold a lot of pressure. And the condition of the paint on the line and union indicates the union has been there a long time, and does not appear to be going anywhere. But there is #7 line on eBay for $55.
The lines are easier to connect if you leave the first end lose while you start the second. However, if that is the only way you can get the second end started, that also means you will put a strain on one or both ends when you tighten them. With a little effort you can reform the lines enough that they will align properly with the injectors, and not be under stress.
We were across country and got a crack in a line next to the machined end. I wrapped the crack with dental floss, and that reduced a spray to a slow drip. A propane torch from Walmart and 45% silver brazing alloy and flux from a welding supply fixed it. I was supposed to braze all the fittings as a preventive, but it is still on the list after a few years and a few more cross country trips.
I bought an 89 E350 for the 7.3 to put in my 84 E350. I did nothing to the engine except clean and paint it. A few years later I swapped the injector pump. I did not encounter anything I would identify as a "vibration damper". Anyone have a picture?
I live in SoCal. I swapped the pump at the end of a dead end road, in a small state park, in W Virginia, during their epoch storm, while blocked in by fallen trees. And doesn't everyone carry a spare pump?