First, I would NEVER consider a patch that is not welded in.  That is at best a temporary fix.  That is such a small area, it would be very simple to make some pieces, even if you had to buy a new taillight panel to cut them from.  I think if I was doing it, I would replace the entire panel.  That way, you don't have to worry about any seams showing.  See my web page: http://www.mustangsteve.com/taillightpanel.html
That one is on my 66, but yours would be just as easy or even easier because it doesn't have the edge going through the taillight hole like the 66 does.  It is such an easy procedure to change it, you can do the whole thing in an afternoon.
If you decided to patch it, I am thinking the curvature would make it more difficult to get smooth, and any small gaps in the weld would allow water from the taillight gaskets to start the rust process all over again.
I vote for a complete replacement.  One afternoon's worth of work and you are done.  Price varies from $103 to $155 depending on coupe/convertible or fastback.  If the price bothers you, then weld in a couple of hand-made patches.  Be sure to butt weld a fitted piece in place.  MUCH easier than fiberglassing !

Thank you both for the input, Yes I will be painting the car, I am leaning towards getting a panel and using it for patches and butt welding them in. Eventhough I'm not doing a full blown resto, I would like to keep as much of the stock sheet metal as possible.

Last edited by Rsmach1 (4/13/2014 8:09 PM)