4" to 4.5" rear wheel bolt conversion on a '64 Valiant?

Install a '73 or newer 7 1/4 or 8 1/4 A body rear end. The 7 1/4 is a direct bolt-in, the 8 1/4 will require your driveshaft to be shortened and larger u bolts and shock plates.
The quick and dirty way is to install wheel adapters or have your existing axles and drums redrilled to the 5x4.5 pattern.