Write XML for Call Web Service using Web method UpdateListItems

I've solved this myself - posting in case it helps anyone else.

Instead of using Call Web Service with the UpdateListItems method from the List B workflow, I added a Call Web Service with web method GetListItems to the List A workflow, after the Create Item In Another Site action.

In order to make the workflow wait until the List B workflow had set the field value I wanted, I created a variable called NewCRNumber in the List A workflow with a null default value. Then I enclosed the Call Web Service and Query XML actions in a Loop with the condition "Workflow Data NewCRNumber is empty".

In the Create Item in Another Site action, the ID of the new item must be stored in a variable of type List ID. I'm sure there's a better way to do this, but since my model code had <Value Type="Text"> I just created another variable called 'text CR ID', and set it equal to the List ID type variable 'CR ID' prior to the Loop action.

In the SOAP editor field of the Call Web Service action I have the following, based on the information in this post:

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Header/>
  <soap:Body>
    <GetListItems xmlns="http://schemas.microsoft.com/sharepoint/soap/">
      <listName>{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxxx}</listName>
      <viewName></viewName>
      <query>
                      <Query>
                             <Where>
                                     <Eq>
                                      <FieldRef Name="ID" />
                                      <Value Type="Text">{WorkflowVariable:text CR ID}</Value>
                                      </Eq>
                            </Where>
                    </Query>
</query>
      <viewFields></viewFields>
      <rowLimit></rowLimit>
      <queryOptions xmlns:SOAPSDK9="http://schemas.microsoft.com/sharepoint/soap/">
 <QueryOptions/>
</queryOptions>
      <webID></webID>
    </GetListItems>
  </soap:Body>
</soap:Envelope>

The result of the Call Web Service action is saved in workflow variable GetListItem_Results, which is then the source for the Query XML action:

I knew to use LinkTitleNoMenu from reading the output in an email sent to myself, as suggested in the link above. Now I had the value, in NewCRNumber, with which I wanted to update the original item in List A.