John, When I make FP to sell. Most don't come with the converter (that's the thingy with the screw)
You just want to throw in the ink cartridge in the pen body so it is there. You do not want to attach it to the nib and puncture the ink and ink the pen. It is really nice the Baron comes with both.
Your client sounds like he has several fountain pens allready. So no doubt, he will have bottle ink to fill the converter. If you put the pen in a box, you might want to throw the ink cartridge in the box, just in case.
There are several ways to fill yuur converter. You can press it into the nib holder and stick the nib in a bottle of ink and suck up the ink into the converter by turning the plunger. I take the converter out of the nib holder and stick the converter into the ink well and suck up the ink, this way you don't get ink all over your pen, just your fingers!
If you make one for yourself, go buy some Private Reserve bottle ink, you will love it.
Anthony