Eugenio
Are you going to replace the HDD with the SSD? if so you could attempt to place the SSD in the MBP and take the HDD and attach it to the External USB and boot from the HDD externally
Use these steps to choose a startup disk with Startup Manager:
- Turn on or restart your Mac.
- Immediately press and hold the Option key. After a few seconds, the Startup Manager appears. If you don't see the volume you want to use, wait a few moments for Startup Manager to finish scanning connected drives.
- Use your mouse or trackpad, or left and right arrow keys to select the volume you want to use.
- Double-click or press the Return key to start up your Mac from the volume you selected.
If you have an optical drive connected to your computer, you can insert an installation disc to see it in Startup Manager. You can also attach FireWire or USB external hard drives that contain an operating system to add to the list of startup volumes. Startup Manager automatically adds bootable volumes as you connect them.
If you have an external time machine back up you can also boot from that and it will give you disk utility options, don't forget to partition the drive and it will take a few hours to re image your drive ( if you MS office it will need to be reactivated)
Paul