Complex sentence: Only two operational Liberty ships survive: the SS "John W. Brown" (following a long career as a school ship and many internal modifications) and the "Jeremiah O'Brien", largely in original condition.
Split into simpler sentences: Only two operational Liberty ships, the SS "John W. Brown" and the "Jeremiah O'Brien", remain. The "John Brown" has had a long career as a school ship and many internal modifications, while the "Jeremiah O'Brien" remains largely in its original condition.