Sounds like you've found most of the traps. The 28 Componon came ( I think ) in two versions. Mine is black with the painted aperture mark ( the Schneider 'disc' ). It's filter size is larger than 40.5, smaller than 46. best I could do.

It is the same design as the 50 Componon, which is - for all intents and purposes identical to your El Nikkor - and is designed for a range of 2x to 20 x. it was intended to project an 18x24 field. Mine is optimal for enlarging at f/6.3, which I suspect is typical.

It should be fine. Small advantages in definition could be gained by a 'real macro lens', but the overall demands of field photography usually buffer lab performance. And since the 28 Componon should be just about free, it should turn out to be a real bargain.

By all means start hunting around the dark corners of Madison for FAX-Nikkors, 'printing nikkors', and so on. You might even turn up a a de-accessioned Microphot/Aristophot etc.

Your work is quite fine: good luck !