Rust is not a problem here in Texas. I have a "temporary" engine in my 240D. I may be interested in your rust bucket to get the engine. Does it use any oil? Is it a stick or automatic? Did you put in a new engine, or rebuild the one you had?
Sorry I don't know much about the 280C. My wife had a '73 250 once, and I had a '68 230. Neither engines were great successes in my mind.
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in