Keep in mind the factory built these cars with a design criteria of lasting no more than seven years (this is codified into US law protecting consumers of capital goods). Today if you find a car that hasn't been restored it will be a rusty hulk with electrical problems. The sheet metal is the hardest to repair and will cost you the most to fix. This is because you can not buy these B-body cars new like you can a mid sixty Mustang, a TriFive Chevy or a first generation Camaro (and soon an early seventies Challenger-Charger body)
Aside from floor pans there are not even a lot of patch panels; and choosing a four door over a two door reduces the availability of finding new sheet metal to replace rusted out parts. So it is in your best interest to find a body that is straight and as rust free as you can. I would avoid anything from the Mid-west (Illinois, Indiana, Michigan, Ohio) or the Northeast (Pennsylvania, Maryland, Virginia, Delaware, Connecticut, New York, Vermont, New Hampshire and Maine) as those populated areas have snowy winters that the local DOT uses salt to deice bridges and roadways. Salt water promotes lots of rust.
There are lots of other snowy areas left in the US but they are not populated heavily enough to pay for road salting so people generally drive four wheel drive vehicles in these areas year round, and used their Impala as a summer cruiser. The Southeastern area of the country is hot and wet with lots of rain fall, so though not as bad rust wise there is a lot more bent sheet metal and a greater chance of a poorly repaired collision damaged car in car projects from this area of the country.
There were not a lot of cars sold in the desert Southwest because not too many people were crazy enough to live there except for southern California which is why prices for a rust free car are rising in general. After Arizona became a retirement Mecca thanks to air conditioned cracker box homes centered around commercial centers there were a lot more cars moved into that area; problem is they were owned by retiring people from the icy Northeast bringing their rolling rust buckets with them.
Because of the mixing of old rust free with newer bondo covered rust buckets I think you will need to physically be there to shop for your project car in person to prevent buying a "pig in poke" (old English saying about buying pork bellies without doing market research to see what was inside the bag). This is an expensive enough hobby already with out making a costly mistake and then adding to it by shipping that mistake to Germany. (by the way to get around import tariffs I recommend buying a car without a motor or tranny and calling the purchase car parts instead of a car). Once the body is repaired, and painted you can buy a crate motor and a tranny to drop into it, as they are just car parts that are easily found on line.