I think you need to define your problem in a little more detail. Exactly what fields do you want to alter, and how can we match them? Also show us a longer sample of the text, including these "other OBX lines" that we have to "account for". We need to know exactly how they relate to the first lines, so we can...what...avoid them? Or insert the text into them too? Your post doesn't make that clear.
And please use [code][/code]
tags around your code, to preserve formatting and to improve readability.
This includes the contents of the files you want to post, as they obviously can have very long lines.
Awk can almost certainly do it, but the devil is in the details.