For anyone else wanting to configure custom memory for MacPro 7,1, here's the entirety of my PlatformInfo->Memory section.
You can copy this in (put it just above UpdateDataHub), and then set CustomMemory = true.
You might need to change DataWidth and TotalWidth if your dmidecode shows different values, and you probably want to change the values for the filled slots to match your real RAM. You may also need to change the BankLocator and DeviceLocator names, if yours don't match these; again, check what dmidecode shows for your own motherboard. But you can use this as a template which might save some time.
Code:
<key>Memory</key>
<dict>
<key>DataWidth</key>
<integer>64</integer>
<key>ErrorCorrection</key>
<integer>3</integer>
<key>FormFactor</key>
<integer>9</integer>
<key>MaxCapacity</key>
<integer>274877906944</integer>
<key>TotalWidth</key>
<integer>72</integer>
<key>Type</key>
<integer>26</integer>
<key>TypeDetail</key>
<integer>128</integer>
<key>Devices</key>
<array>
<dict>
<key>AssetTag</key>
<string></string>
<key>BankLocator</key>
<string>NODE 1</string>
<key>DeviceLocator</key>
<string>CPU1_DIMM_A1</string>
<key>Manufacturer</key>
<string>Patriot</string>
<key>PartNumber</key>
<string>ViperSteel</string>
<key>SerialNumber</key>
<string></string>
<key>Size</key>
<integer>32768</integer>
<key>Speed</key>
<integer>3600</integer>
</dict>
<dict>
<key>AssetTag</key>
<string></string>
<key>BankLocator</key>
<string>NODE 1</string>
<key>DeviceLocator</key>
<string>CPU1_DIMM_A2</string>
<key>Manufacturer</key>
<string>EMPTYDIMM</string>
<key>PartNumber</key>
<string>EMPTYDIMM</string>
<key>SerialNumber</key>
<string>EMPTYDIMM</string>
<key>Size</key>
<integer>1</integer>
<key>Speed</key>
<integer>1</integer>
</dict>
<dict>
<key>AssetTag</key>
<string></string>
<key>BankLocator</key>
<string>NODE 1</string>
<key>DeviceLocator</key>
<string>CPU1_DIMM_B1</string>
<key>Manufacturer</key>
<string>Patriot</string>
<key>PartNumber</key>
<string>ViperSteel</string>
<key>SerialNumber</key>
<string></string>
<key>Size</key>
<integer>32768</integer>
<key>Speed</key>
<integer>3600</integer>
</dict>
<dict>
<key>AssetTag</key>
<string></string>
<key>BankLocator</key>
<string>NODE 1</string>
<key>DeviceLocator</key>
<string>CPU1_DIMM_B2</string>
<key>Manufacturer</key>
<string>EMPTYDIMM</string>
<key>PartNumber</key>
<string>EMPTYDIMM</string>
<key>SerialNumber</key>
<string>EMPTYDIMM</string>
<key>Size</key>
<integer>1</integer>
<key>Speed</key>
<integer>1</integer>
</dict>
<dict>
<key>AssetTag</key>
<string></string>
<key>BankLocator</key>
<string>NODE 1</string>
<key>DeviceLocator</key>
<string>CPU1_DIMM_C1</string>
<key>Manufacturer</key>
<string>Patriot</string>
<key>PartNumber</key>
<string>ViperSteel</string>
<key>SerialNumber</key>
<string></string>
<key>Size</key>
<integer>32768</integer>
<key>Speed</key>
<integer>3600</integer>
</dict>
<dict>
<key>AssetTag</key>
<string></string>
<key>BankLocator</key>
<string>NODE 1</string>
<key>DeviceLocator</key>
<string>CPU1_DIMM_C2</string>
<key>Manufacturer</key>
<string>EMPTYDIMM</string>
<key>PartNumber</key>
<string>EMPTYDIMM</string>
<key>SerialNumber</key>
<string>EMPTYDIMM</string>
<key>Size</key>
<integer>1</integer>
<key>Speed</key>
<integer>1</integer>
</dict>
<dict>
<key>AssetTag</key>
<string></string>
<key>BankLocator</key>
<string>NODE 1</string>
<key>DeviceLocator</key>
<string>CPU1_DIMM_D1</string>
<key>Manufacturer</key>
<string>Patriot</string>
<key>PartNumber</key>
<string>ViperSteel</string>
<key>SerialNumber</key>
<string></string>
<key>Size</key>
<integer>32768</integer>
<key>Speed</key>
<integer>3600</integer>
</dict>
<dict>
<key>AssetTag</key>
<string></string>
<key>BankLocator</key>
<string>NODE 1</string>
<key>DeviceLocator</key>
<string>CPU1_DIMM_D2</string>
<key>Manufacturer</key>
<string>EMPTYDIMM</string>
<key>PartNumber</key>
<string>EMPTYDIMM</string>
<key>SerialNumber</key>
<string>EMPTYDIMM</string>
<key>Size</key>
<integer>1</integer>
<key>Speed</key>
<integer>1</integer>
</dict>
<dict>
<key>AssetTag</key>
<string></string>
<key>BankLocator</key>
<string>NODE 1</string>
<key>DeviceLocator</key>
<string>DIMM_EMPTY</string>
<key>Manufacturer</key>
<string>EMPTYDIMM</string>
<key>PartNumber</key>
<string>EMPTYDIMM</string>
<key>SerialNumber</key>
<string>EMPTYDIMM</string>
<key>Size</key>
<integer>1</integer>
<key>Speed</key>
<integer>1</integer>
</dict>
<dict>
<key>AssetTag</key>
<string></string>
<key>BankLocator</key>
<string>NODE 1</string>
<key>DeviceLocator</key>
<string>DIMM_EMPTY</string>
<key>Manufacturer</key>
<string>EMPTYDIMM</string>
<key>PartNumber</key>
<string>EMPTYDIMM</string>
<key>SerialNumber</key>
<string>EMPTYDIMM</string>
<key>Size</key>
<integer>1</integer>
<key>Speed</key>
<integer>1</integer>
</dict>
<dict>
<key>AssetTag</key>
<string></string>
<key>BankLocator</key>
<string>NODE 1</string>
<key>DeviceLocator</key>
<string>DIMM_EMPTY</string>
<key>Manufacturer</key>
<string>EMPTYDIMM</string>
<key>PartNumber</key>
<string>EMPTYDIMM</string>
<key>SerialNumber</key>
<string>EMPTYDIMM</string>
<key>Size</key>
<integer>1</integer>
<key>Speed</key>
<integer>1</integer>
</dict>
<dict>
<key>AssetTag</key>
<string></string>
<key>BankLocator</key>
<string>NODE 1</string>
<key>DeviceLocator</key>
<string>DIMM_EMPTY</string>
<key>Manufacturer</key>
<string>EMPTYDIMM</string>
<key>PartNumber</key>
<string>EMPTYDIMM</string>
<key>SerialNumber</key>
<string>EMPTYDIMM</string>
<key>Size</key>
<integer>1</integer>
<key>Speed</key>
<integer>1</integer>
</dict>
</array>
</dict>