[Zubersoft]

I'm just using abc2svg under the covers, however, I set the margins myself right now. I dynamically insert them at the top of a copy of the abc file. So it's possible if you set them below that, you could override them, but I haven't tested that. The units should be the same as abc, but a page scaling factor is applied based on the density of the screen, so that may have an impact on the margins (I don't know how abc2svg handles the relationship between the margins and scaling factor). 

I don't have control over how abc2svg renders chords, so I can't speak to what's happening there. I don't think I observed that with any of the files I tested with. It's helpful to post a file as an example if you are encountering problems.

Mike