Need Help! Proper Way To Smooth Body Lines

I've watched this forum for quite some time, but this is my first post! Want to thank you guys for all the great info over the years. This forum has been a great resource throughout my restoration. I am in the process of finally getting paint on my 65 fastback, and I am getting pretty close to finishing up the body work. I want to smooth some of the body lines, but I am unsure of the proper way to do this. The areas I would like to smooth are where the rear valance meets with the rear quarter panel, where the quarter panel extensions meet up with quarters and the seam where the rocker panel meets with the body just in front of the rear wheels. Here are my thoughts so far. Since it had seam sealer originally, I am guessing there will be a certain degree of flex in the joint where the rocker meets the body, so I am unsure how to smooth this seam without it cracking. I have some Norton 2K epoxy seam sealer left over from seam sealing the rest of the car. Supposedly you can sand this stuff (never tried sanding it), could I just fill the seam with this stuff and sand it down? Anybody sand this stuff before? Does it sand well or even sand at all? Is there a better way to achieve the smooth look? For the rear valance and quarter panel extensions, I plan to use a good quality panel bonding adhesive to attach them to the car. Yet I am unsure of the proper way to fill this joints between the panels. Would you just use something like kitty hair topped with regular filler? I have got the panels to fit the car fairly well, so there isn't that much of a gap to fill. Again, given it is a unibody I am concerned body flex might put stress on the joint and cause body filler to crack. Is there a better way to do this? I have seen Mustang Depot attach fiberglass panels to metal with Norton Speed Grip urethane structural adhesive and they say this stuff can be used like a body filler and also remains flexible, would that be a good way to go? Would be convenient since I already have the Norton 2K gun from the seam sealer... If the 2K epoxy seam sealer sands well, could I use that? Or are my fears of the body filler cracking unfounded? Is there a better way to do this? Thanks in advance for any help, I can assure you it is greatly appreciated!!

horse sence said:

the rear valance can be welded down the seam and ground smooth. it should be welded so it doesnt crack later. the quarter to rocker ,the same ,welded or it will crack later. i have yet to see a set of end caps that didnt either crack or show a line after being bonded on. the pot metal end caps expand different from the steel quarter and a line or cracking will appear sooner or later.

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Thanks for the response! Have you ever had any problems with cracking along a welded seam? I would prefer to weld the rocker and rear valance, but I heard from some local old school car guys the flex in unibody cars causes even welded seams to crack. One of the guys had a 66 fastback and welded his rocker seams and they both cracked. They said leading was only way to go. I also saw another post a few weeks back that said the same about welded seams cracking. That's why I was thinking of going with a modern product that supposedly remains flexible even after it cures, like the norton 2k epoxy or urethane products I mentioned above. Was it maybe just those welds weren't proper or is cracking paint a risk you have to take to get the seamless look? Also I am unsure of how to weld pot metal, would you just braze it? Is there some other method to weld it? Thanks again! I appreciate you guys sharing your wisdom and experience!

Welding it is! Thanks for the help! I will post some pics when i get it done!