There is no magical product that can truly deal with your situation. It appears your car has been in some very bad climates and/or had salt and other such stuff eat away at it. It takes a serious commitment of time, money, etc - to truly resolve what I'm seeing.
What needs to happen is to pull the body from the frame, have the bottom of the body blasted to "see what you have left" - and the same goes for the frame. Once the body is off the frame, you can pretty easily determine if it pays to restore the frame (depending on how much structural damage and where), versus finding a new one.
All metal work that you need to farm out (floor pans and frame) is expensive - given today's shop rates, but there really isn't much of an alternative if you desire to "fix" the issues for the long term. There are a millions ways to ignore the real issues (serious rust) and put band-aids on it - but none of them are really viable (given what I'm seeing).
Unless you have the equipment, time, facilities and skills, both the body and the frame will require outside services . . . and they are never cheap.
If this is a car you want to keep, then it may be worth putting the $$$ into it . . . just understand what you're getting into (get real estimates) - before you head down the path.
From your description, it is a 39 Sedan - and I'm going to hate to say this, but - you need to decide how much you want to invest in it . . . as my guess is that unless you're capable of doing a lot of the work yourself, that you'll put far more into it, than many of us would want too.
With that said, most of us are NOT building wise "investments" - we're spending money on cars and hobbies that we enjoy - we know that in the end, we'll probably be "upside down" as far as the ultimate value if we desire to sell what we 'invested' in. We do it because we love these cars, we love to drive them and we want to see them on the road in as best of condition as possible (given time, money, emotional value, etc).
Just calling it out as I believe it to be . . . not trying to put a wet blanket on your fire. I hope you find a way to continue down your path, get it all sorted out as best as possible, make sure it is safe and that it can "live" many more decades.
Best of luck!