Need some help from a rust guru!

Many thanks to all for the input. Your tips are valuable and will help with the project going forward.

Don't bother with anything like that. You'll just trap water or dust. Sounds like you have access to a welder anyway. Get some 18 ga metal and patch it.

I do have a stick welder, but if I'm not the worst welder on the planet I could certainly give the winner a run for their money. If this and all the rest of the sheet-metal welding is beyond my capabilities, I will farm out the work.

When you talked about getting the car back together and getting it on the road and putting things back together in my mind I thought you were going in the wrong direction. This is your dream car that it needs to be done right. with that said I would be blowing it all apart every last nut and bolt... Fixing all the body work from the inside and getting the body perfect. Even up into sandblasting or like they're saying glass beading. Get an epoxy coat on the body itself and then start doing the suspension which is probably all rotted anyways. Then work your way up to the fenders the interior and finally the motor and transmission. If this is the one then this is the one.do it right the first time or you'll never be satisfied... My-2

A couple of valid points Mr. J Par, and I get it. Part of the problem was the initial hunt for the Dart. I already had a complete 383, 4-speed, and 8-3/4 for the car before I found it. I figured I was going to find a slant car to transplant the drive train, or maybe a 273 car. Never in my wildest dreams did I think I was going to find a very affordable, running, 340/727 car, albeit still with the original 7.25 rear end. That makes the situation more interesting. Now that I'm the proud owner of a 340 car, I may decide a healthy SB is enough for my street-fun desires and the BB will move on to another owner. Or maybe I decide to do the BB anyway. Maybe the auto is enough fun and the 4-speed hits the auction block. At this point, I'm going to get this thing street worthy and drive it for a while to decide what I really want to do. I'm stopping obvious deterioration and keeping the car indoors while I sort things out. Some stuff it doesn't make any difference when it gets done. Like the lights, horn, heater, ignition switch, brakes, etc all don't work. I'm aware I will be somewhat inefficient by doing things out of order, but I don't want to start a looooooooooong project at the moment. Get it driving, sort things out, decide where I want to go, then finish the car. It is indeed the dream car, and it will be done right in the end.