salvage question on parts removal

I'm trying to help a guy put a v-8 in a 75 duster-- after looking his car over -- it will need major rust repair in critical areas. (T bar mounts have over quarter size flaking rust spots both sides)

I have this 73 dart sport that has great cross member & frame rails & inner fenders--- how to remove this stuff quickly so the 75 duster can live?

thanks Lawrence