This procedure works perfectly as of this date - I've upgraded two MacBook 3,1 laptops this way. Use MLPostFactor, not MacPostFactor, which no longer works for Mountain Lion (as of 2.0.x).
First, download MLPostFactor 0.3:
http://iusethis.luo.ma/mlpostfactor/MLPostFactorV0.3.zip
Then, follow the instructions here:
For your convenience, here are the contents of the plist files for the SystemVersion.plist updates referenced in the video:
10.8.4:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>ProductBuildVersion</key>
<string>12E55</string>
<key>ProductCopyright</key>
<string>1983-2013 Apple Inc.</string>
<key>ProductName</key>
<string>Mac OS X</string>
<key>ProductUserVisibleVersion</key>
<string>10.8.4</string>
<key>ProductVersion</key>
<string>10.8.4</string>
</dict>
</plist>
10.8.5:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>ProductBuildVersion</key>
<string>12F45</string>
<key>ProductCopyright</key>
<string>1983-2013 Apple Inc.</string>
<key>ProductName</key>
<string>Mac OS X</string>
<key>ProductUserVisibleVersion</key>
<string>10.8.5</string>
<key>ProductVersion</key>
<string>10.8.5</string>
</dict>
</plist>
First, download MLPostFactor 0.3:
http://iusethis.luo.ma/mlpostfactor/MLPostFactorV0.3.zip
Then, follow the instructions here:
For your convenience, here are the contents of the plist files for the SystemVersion.plist updates referenced in the video:
10.8.4:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>ProductBuildVersion</key>
<string>12E55</string>
<key>ProductCopyright</key>
<string>1983-2013 Apple Inc.</string>
<key>ProductName</key>
<string>Mac OS X</string>
<key>ProductUserVisibleVersion</key>
<string>10.8.4</string>
<key>ProductVersion</key>
<string>10.8.4</string>
</dict>
</plist>
10.8.5:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>ProductBuildVersion</key>
<string>12F45</string>
<key>ProductCopyright</key>
<string>1983-2013 Apple Inc.</string>
<key>ProductName</key>
<string>Mac OS X</string>
<key>ProductUserVisibleVersion</key>
<string>10.8.5</string>
<key>ProductVersion</key>
<string>10.8.5</string>
</dict>
</plist>