custom keyboard

I have created a custom Dvorak keyboard layout that I have used successfully under Ubuntu 16.04. Now I am trying to get it to work with Ubuntu 20.04.

Here are my steps:

1. I copy my layout file to /usr/share/X11/xkb/symbols/dv-mac
2. I add the following line to /usr/share/X11/xkb/rules/xorg.lst

  dv_mac          us: Dvorak extended (similar to Mac OS X)

3. I add the following to the <layoutList> sections of /usr/share/X11/xkb/rules/xfree86.xml and /usr/share/X11/xkb/rules/evdev.xml

      <layout>
        <configItem>
        <name>dv-mac</name>
        <shortDescription>Dvorak</shortDescription>
        <description>Dvorak</description>
        <languageList>
          <iso639Id>eng</iso639Id>
        </languageList>
        </configItem>
        <variantList />
      </layout>

Here's where I put this block, as the first item in the <layoutList>, just after the <modelList>, at around line 1335:

...
    <model>
      <configItem>
       <name>teck229</name>
       <description>Truly Ergonomic Computer Keyboard Model 229 (Standard sized Alt keys, additional Super and Menu key)</description>
       <vendor>Megawin Technology</vendor>
     </configItem>
    </model>
  </modelList>
  <layoutList>

    <layout>
      <configItem>
        <name>dv-mac</name>
        <shortDescription>Dvorak</shortDescription>
        <description>Dvorak</description>
        <languageList>
          <iso639Id>eng</iso639Id>
        </languageList>
      </configItem>
      <variantList />
    </layout>

    <layout>
      <configItem>
        <name>us</name>
        <!-- Keyboard indicator for English layouts -->
        <shortDescription>en</shortDescription>
        <description>English (US)</description>
        <languageList>
          <iso639Id>eng</iso639Id>
        </languageList>
      </configItem>
...

I have noted that I use dv_mac in the xorg.lst file and 'dv-mac` (with a hyphen instead of an underscore) elsewhere, but apparently this worked both on Ubuntu 16.04 and a previous version of Ubuntu 20.04 that I installed.

However, this time, I cannot get the entry for my Dvorak keyboard to appear in the Language and Region settings.

Any help in finding where I have gone wrong this time will be much appreciated.