[Arran]

You can call me crazy but I have seen much worse. That chassis looks like most of the rust is a light to medium scale, if it was really bad it would have thick, dark scabs all over it. Step number #1 is to take lots of pictures and diagrams and start taking it apart. If you can get a hold of some Evapo Rust or a reasonable facsimile, you should be able to dunk the parts in it, minus coils and transformers, apparently it does not effect copper, aluminum or brass so you could leave the sockets in place. If you can't find Evapo Rust (or facsimile) you can also try a mixture of water and molasses, both work by chealation and are NOT acidic.
You could also try electrolysis for stripping rust, but you would have to remove any copper, aluminum, or brass parts from the chassis and other bits first. Well you may get away with the copper and brass but not the aluminum. That will get it down to bare metal, it will even take paint off if there is any. But two things you need are a low voltage high current power supply, that puts out a clean DC current, If you use a battery charger you will need to add a filter cap to the output. You will also need a sacrificial anode with a large surface area. For an electrolyte you can use baking soda, washing soda, or trisodium phosphate, about a cups worth in a gallon or more of water. Negative side of supply connects to the part you are stripping, positive goes to the sacrificial anode.
Regards
Arran