1976 240D Engine Rust

Was virtually given a 1976 240D with fine body and just about everything else except the engine. Cannot crank by hand and rust shows when valve cover removed. Am thinking this engine is a lost cause, but am asking if there is some old mechanics wisdom about freeing a rusty engine. I found one site for old Ford tractors that claimed white vinegar in the cylinders would loosen rust. Hmmm ..?

Last resort would be a different 616.916 long block. Any sources Kent?