Lee... that is not as hopeless as it looks.
There is a gunsmith, Mark Novak, that posts restoration videos on Youtube and he's figured out how to deal with rust.
Utilize the rust bluing process.... the old school way of bluing firearms.
The rust bluing process is to apply a solution to intentionally rust a firearm (the way that the A-5 looks), then boil it to convert the red oxide rust to black oxide.
The gun is carded with a soft wire wheel... and what's underneath is a nice blue/black.
That A-5 already has the 1st stage of the rust bluing process done, the gun doesn't look pitted.
The wood looks completely recoverable too.
I've done rust bluing, stuff coming out of the rust cabinet looks awful, it's surprising how it turns out after boiling and carding.
Checkout this video where he turns a rusty Winchester 1887 into a thing of beauty: