Building a body line help needed

Working on a 66 dodge dart. The body actually isnt that bad, however I made things worse by deciding not to use the original body belt trim which means weld the holes shut that were for the fasteners. Originally I filled the holes with the 3M 8115 body panel glue. But after talking to some body guys and hearing that in a few years the material may shrink and leave a visible spot I decided to do the permanent weld the holes shut fix. Of course that distorts the metal some so now there is a little body work needed around every hole. Before I welded them shut I tapped each hole in some so there would be less grinding before filling and sanding.
Now my real issue is how do I rebuild the body line on the front fender. Im talking about where the trim belt went on. The pic below you can see the area I am talking about. The area where the delt trim was is only about 1 1/8" wide. It is raised off the body until it blends into the fender just behind the 4th hole. The two lines, (top and bottom of that area is where i am having the line issue.) Its a slightly rounded line. Not a sharp line and where the body filler has to be put i need to know the best method to keep that line straight and correct height. What is the best method for sanding and making the lines straight. DSCN1664.JPG
Ive seen how tape can be used but do I start on the flat area or the side area. Heres where I am right now.
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It looks like the line is there but its not straight and it seems like all im doing is putting on filler and then sanding it off. I also had to weld the 4 other holes shut which makes for more area to add filler and sand. I hope this makes sense and I look forward to hearing your methods so I can get this area done.
Thanks in advance, Rod