using a maven plugin and an assembly job.xml a job.jar is created with all dependencies including transitive ones. This job.jar is in mahout/spark/target and is included in the classpath when a Spark job is run. This allows dependency classes to be found at runtime but the job.jar include a great deal of things not needed that are duplicates of classes found in the main mrlegacy job.jar. If the job.jar is removed, drivers will not find needed classes. A better way needs to be implemented for including class dependencies.
I'm not sure what that better way is so am leaving the assembly alone for now. Whoever picks up this Jira will have to remove it after deciding on a better method.