How to set up multi cluster spark without hadoop on Google Compute engine
As explained in the comments by @Emre, there is a python script on github which you can use to set up a cluster of whatever size you like: Spark Cluster on Google Compute Engine | Ido Green.  It allows you to specify the instance type to use for the workers (slaves) and separately what to use for the master.

Note that it uses gcutil, which is deprecated in favor of gcloud compute