Je vous confie la manip telle quelle, extraite de xda developpers, pour installer le Google Play.
"Here is how to install a new and working Google Play Store:
1. Download "Vending.apk".
2. Copy Vending.apk to \system\app\ folder in your phone by using ES File Explorer in root explorer mode with system file mounted.
3. Change permission of Vending.apk to Read/Write for Owner; Read for others (rw-r--r--)
4. Shutdown your phone.
5. Switch on your phone, you will see Google Play Store app, and Enjoy !"