{
  "goto_section":"payment",
  "update_section":{
     "name":"payment-method",
     "html":"... HTML & JS for payment methods ...",
     "review":"... HTML & JS for review box ..."
   }
}

<checkout_onepage_paymentmethod>
    <remove name="right"/>
    <remove name="left"/>

    <block type="checkout/onepage_payment_methods" name="root" output="toHtml" template="checkout/onepage/payment/methods.phtml">
        <action method="setMethodFormTemplate"><method>purchaseorder</method><template>payment/form/purchaseorder.phtml</template></action>
        <block type="core/template" name="checkout.onepage.payment.methods.scripts" as="scripts" />
        <block type="core/template" name="checkout.onepage.payment.methods.additional" as="additional" />
    </block>

    <block type="checkout/onepage_review_info" name="review.update" template="checkout/onepage/review/info-sidebar.phtml">
        <action method="addItemRender"><type>default</type><block>checkout/cart_item_renderer</block><template>checkout/onepage/review/item.phtml</template></action>
        <action method="addItemRender"><type>grouped</type><block>checkout/cart_item_renderer_grouped</block><template>checkout/onepage/review/item.phtml</template></action>
        <action method="addItemRender"><type>configurable</type><block>checkout/cart_item_renderer_configurable</block><template>checkout/onepage/review/item.phtml</template></action>
        <block type="checkout/cart_totals" name="checkout.onepage.review.info.totals" as="totals" template="checkout/onepage/review/totals.phtml"/>
    </block>
    </checkout_onepage_paymentmethod>