Are you treating with Metal Ready before painting (POR15)?

Yep!
Don't underestimate the value of gussets to eliminate flexing at stress points that would crack over time.

Yes.

After I patch section "B" , how do I protect the inside of that section?

Repairs completed...now I can finish up my fuel line relocation and drive again.Click to view attachment
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Last shot:
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The floor pan repair would have looked much better if it had been on the inside of the lip and it would have shed water better. Be sure and metal prep the welds and clean them really well and epoxy prime them, a brush will work ok, and then seal them really well and more epoxy primer or you will be doing it again. Repairs don't need to look like they were just slapped on top of old metal.

"Function Before Form". I don't weld so I was at the mercy of somebody else. NO offense, and I appreciate the feedback, but I really don't care how good it looks...the car is for driving and making me smile, not concours. Not a DD so unless I miscalculate the weather, she will never be shedding water again. How about Metal Prep and POR15? What would you seal the seams with? One person said Bondo, but me thinks not. Seam sealer?

Took 40 years in all kinds of weather to get to were she was. Now she's in a heated, dry garage and will not go out in rain or snow. I'm 57 so I'm betting I'll never have to do it again!

Damn I've got no idea how to quote and change color in the quote so you are way ahead of me. I'm pretty sure someone else will want your car after you are through with it and it will probably look really good, it's just that to me the little details are what really makes a nice car. I'm 65 and hope most things I do will outlast me but unless they end up in the lake someone else will get them and maybe they won't have to do what I've done over. I have actually needed to do some things on the same cars more than once (usually body work) and I really hate it. I have kept most of my cars a long time.

I like dp 40,90,70 but I think now there might be better epoxy primers since ppg took the lead out. I have used por15 a lot and have decided it's ok on suspension parts but not for floorboards or top coating anything serious. I did a jeep pickup under the wheelwells and then undercoated them and all the undercoat has come loose. Also I did the replaced floors and the bedliner has just come off of over the por15. I did the innerfender front fenders inside and out and the rad support front and back and used the tiecoat blue primer restomotive reccommended over it then top coated and that has held up ok. The cost was too much for the application. Good epoxy primer seems to me to be the best. It seals better and sticks better than anything I have found sofar. I even used it (dp90) to paint the aluminum floor threshold trim after it was beadblasted and it hasn't worn through or chipped yet from several years of climbing in and out with muddy boots.

Why was the triangle put on before the patches? It just looks so wrong!

Patched the long first (of course). Then did the triangle , then patched the firewall hole. Unless I run over some "too knowledgeable" 914 nut, nobody will ever see it.

And remember...the damn car is "Not so special" anyway.