OS 9 dos not require cloning software in order to copy a drive - a drag-and-drop copy is sufficient.
Add the new drive as a second drive - the G4 should be pre-equipped to accept a second drive. Jumper the second drive as Slave, and make sure the original drive is jumpered as Master (some Western Digital drives are jumpered as Single when there is no second drive, and need to be changed to Master when a second drive is added),
Format the new drive using Drive Setup - use the Mac OS Extended format.
Once the new drive is ready, drag the icon of the original drive to the new drive's icon and drop it in - the entire contents of the original drive will be copied to the new drive, and placed into a folder on the new drive; this folder will be named the same as the original drive.
Once the copying is complete, open the new drive and drag the System Folder, Utilities folder, Documents folder, and Applications folder out of the enclosing folder so that they are at the root level of the new drive (the root level is what you see when you first open the drive),
Make sure the System Folder displays the Mac OS glyph - this indicates it is "blessed".
If that's OK, then test boot to the new drive - use the Startup Disk control panel to select it, then restart.
Noye - some aliases may need to be 'fixed' on the new drive. This can include an alias to Sherlock in the Apple Menu Items folder in System Folder, a few items in the Application Support folder in System Folder, and any you may have created for your own convenience.