private Component buildInitalValuePanel() {
		initialValueLabel = new GDLabel("Initial Value");
		initialValueField = new RegisterField(8, null, false);
		initialValueField.setName("Initial Value");
		initialValueField.getAccessibleContext().setAccessibleName("Initialized Block Value");
		initialValueField.getAccessibleContext()
				.setAccessibleDescription("Enter the initial value for every byte in this block");

		initialValueField.setChangeListener(e -> initialValueChanged());

		JPanel panel = new JPanel(new PairLayout(4, 10));
		panel.setBorder(BorderFactory.createEmptyBorder(5, 7, 4, 5));
		panel.add(initialValueLabel);
		panel.add(initialValueField);
		return panel;
	}
Define the Main panel for the dialog here.
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/memory/AddBlockDialog.java