I always thought of the DC-4 as a DC-3 with two added engines and somewhat improved hydros.
What are the actual differences between them?
The DC-4 was a totally new design in all respects, as can be seen from the planform diagrams (wiki)
The DC-4 was larger, and structurally totally different:
All in all a larger aircraft, designed from scratch, implementing more modern features of a later age.