Waterman #5 semi flex nib

I have never tried this match up and don't even own a Jowo nib, but I *can* tell you that more often than not vintage nibs are much thinner at the tail than modern nibs, especially modern steel nibs. I would expect that the nib will *not* be tight in that feed/sleeve setup, but the only way to know for certain is to try.

Another thing to be aware of is that nib size numbers are not standardized between manufacturers... You'll want to look carefully at how the curvature of the nib matches the feed diameter. Even a fairly small difference in these dimensions can either damage or upset the adjustment of a flexible gold nib!