EDIT: If you DONT like this solution pls add a comment!
First of all finish the EBONY COAST level.
Then start it again in free mode and get the J-bomb Robot.
-credit for this video goes to sublym0nal-
here is a video where you can see how to find the heads needed for the achievement. You need the J-Bomb robot to find an smash those Heads.
You need to finish the level through the yellow truck and wait for the stats screen at the end of the level :)
Hope this helps :D
(the time stamps did not work proper)
The achievement Starts by 4m 18s
-all videos except from the first one are my gameplay-