Rusty
Refine your search to posts by user MPandC (Robert). He won't lead you astray. I would agree with Dongray about using a butt weld. On a quarter panel that welds to a door pillar, it makes it relatively easy to line up and scribe the patch panel for cutting. Then trim it a tiny bit large and cut down to fit closely. As long as you can get a dolly behind the joint area, that's the way to go. Robert has posted an example of a "ghost line" that's visible in a finished panel that had a lap joint patch.
I'm definitely a disciple of Robert's procedures (although I'm nowhere as talented as he is.) I've tried to take pictures of fitting and welding patches. You're welcome to scan through the photos linked in my signature to see what I've done.

Kevin
1951 Chevy 3100 work truck
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Photos
1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.