Line pressure is low as it goes through the cooler into the pan. A hose clamp and a piece of rubber fuel line will work. That said it is easy to replace the lines. You can buy them pre-bent or as coiled tube that you straighten out and cut to length then add fittings before you flare the tubes. This is an application (one of few on a car that you can use braided stainless steel hose if you wanted to go with AN fittings.
As to who is on top it doesn't matter it is fluid entering a small radiator inside the main radiators tank. There are no one way valves to control direction of flow.
I wouldn't use a compression fitting on a rusted line that is already crumbling. It will not seal.