Android keyboard custom layout

I need a custom keyboard that uses an existing open source keyboard engine. In other words, the brains behind the android keyboard should stay the same. There is no need to reinvent the code that helps with word prediction. All I need is a new layout for the for the characters / numbers keyboard. The placement of the keys must be identical to that of the alphabetical keyboard. In fact it is only the middle row of the second row from the top that needs changing to match the number of keys and width of the alphabetical keyboard. I will specify what symbols should appear on that row. The keyboard must be an apk that can be installed as an extra keyboard input option in the system settings. This must be compatible with the Galaxy S3, gingerbread or jelly bean.