Yes, I remember considering the Lindheimera texana previously and rejected it as a match. My plant normally reaches 4' in poor conditions, and given a little water can exceed 6'. It also has a rather tangled, shrubby growth habit. Sunflowers seem to have too many petals and a tidier center than mine. I still don't think we have an exact match, but it is getting close! If the wind and rain move out, I will try for more revealing pictures - including of the seeds.
Here is another old picture of the bloom which also makes the form of the leaves easier to see.
