No se puede hacer como lo planteas: esos números de las variables no son "índices".
Supongo que son componentes visuales, por el método setEnable.
Sería mejor que explicases con detalle el diseño que tienes.

Puedes añadir los botones en una List cuando los creas:

final List<JButton> botones = new ArrayList<>(27);

1- Inicializo y coloco en su sitio los 27 botones....
letra1=new JButton("A");
letra1.setBounds(270,200,30,30);
letra1.setMargin(new Insets(1,1,1,1));
letra1.setEnabled(false);
add(letra1);
letra1.addActionListener(this);
botones.add(letra1);

... así sucesivamente para todos los 27 botones.

con el método siguiente puedes ponerlos todos en enabled o disabled con facilidad.

public void setBotones(boolean isEnable){
for(JButton boton : botones){
boton.setEnable(isEnable);
}
}

Existe otra manera de "localizar" componentes en un contenedor.
En el test que sigue, se ve cómo hacerlo.

public class NewJFrame extends javax.swing.JFrame {

/** Creates new form NewJFrame */
public NewJFrame() {
initComponents();
}

public static <T extends JComponent> List<T> getDescendantsOfType(Class<T> clazz, Container container, boolean nested) {
final Component[] components = container.getComponents();
final List<T> tList = new ArrayList<>(components.length);
for (Component component : components) {
if (clazz.isAssignableFrom(component.getClass())) {
tList.add(clazz.cast(component));
}
if (nested || !clazz.isAssignableFrom(component.getClass())) {
tList.addAll(SwingUtils.<T>getDescendantsOfType(clazz, (Container) component, nested));
}
}
return tList;
}

/**
@param args the command line arguments
*/
public static void main(String args[]) {
/* Create and display the form */
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new NewJFrame().setVisible(true);
List<JButton> botones = getDescendantsOfType(JButton.class, jPanel1, false);
for (JButton boton : botones) {
System.out.println("boton " + boton.getText());
}
}
});
}

/** This method is called from within the constructor to
initialize the form.
WARNING: Do NOT modify this code. The content of this method is
always regenerated by the Form Editor.
*/
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() {

jPanel1 = new javax.swing.JPanel();
jButton1 = new javax.swing.JButton();
jButton2 = new javax.swing.JButton();
jButton3 = new javax.swing.JButton();
jButton4 = new javax.swing.JButton();
jTextField1 = new javax.swing.JTextField();

setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

org.openide.awt.Mnemonics.setLocalizedText(jButton1, java.text.MessageFormat.format(java.util.ResourceBundle.getBundle("utils/Bundle").getString("NewJFrame.jButton1.text"), new Object[] {})); // NOI18N

org.openide.awt.Mnemonics.setLocalizedText(jButton2, java.text.MessageFormat.format(java.util.ResourceBundle.getBundle("utils/Bundle").getString("NewJFrame.jButton2.text"), new Object[] {})); // NOI18N

org.openide.awt.Mnemonics.setLocalizedText(jButton3, java.text.MessageFormat.format(java.util.ResourceBundle.getBundle("utils/Bundle").getString("NewJFrame.jButton3.text"), new Object[] {})); // NOI18N

org.openide.awt.Mnemonics.setLocalizedText(jButton4, java.text.MessageFormat.format(java.util.ResourceBundle.getBundle("utils/Bundle").getString("NewJFrame.jButton4.text"), new Object[] {})); // NOI18N

jTextField1.setText(java.text.MessageFormat.format(java.util.ResourceBundle.getBundle("utils/Bundle").getString("NewJFrame.jTextField1.text"), new Object[] {})); // NOI18N

javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
jPanel1.setLayout(jPanel1Layout);
jPanel1Layout.setHorizontalGroup(
jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel1Layout.createSequentialGroup()
.addContainerGap()
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel1Layout.createSequentialGroup()
.addComponent(jButton1)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
.addComponent(jTextField1, javax.swing.GroupLayout.DEFAULT_SIZE, 301, Short.MAX_VALUE))
.addGroup(jPanel1Layout.createSequentialGroup()
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jButton2)
.addComponent(jButton3)
.addComponent(jButton4))
.addGap(0, 0, Short.MAX_VALUE)))
.addContainerGap())
);
jPanel1Layout.setVerticalGroup(
jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel1Layout.createSequentialGroup()
.addGap(22, 22, 22)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(jButton1)
.addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGap(22, 22, 22)
.addComponent(jButton2)
.addGap(22, 22, 22)
.addComponent(jButton3)
.addGap(22, 22, 22)
.addComponent(jButton4)
.addContainerGap(18, Short.MAX_VALUE))
);

getContentPane().add(jPanel1, java.awt.BorderLayout.CENTER);

pack();
}// </editor-fold>

// Variables declaration - do not modify
private javax.swing.JButton jButton1;
private javax.swing.JButton jButton2;
private javax.swing.JButton jButton3;
private javax.swing.JButton jButton4;
private static javax.swing.JPanel jPanel1;
private javax.swing.JTextField jTextField1;
// End of variables declaration
}