Just for laughs 150.00$ 1967 383

Go to your nearest farm supply store, get a stock tank big enough to drop a block into and 2 gallons of molasses. Lower the entire engine in, pour in the molasses, and fill rest of the way with water. After a few days of soaking most of the surface rust should be loose, so lift it out, scrub off all you can, lower it back in. Repeat until it's fresh clean cast iron. Molasses is an agent of chelation for iron, which means it reverses oxidation.

Or...since 383's are cheap and easy to find - buy a nicer one.