CPU only nodes' names start with GM and the GPU ones start with OB (Octane Benchmark). If you can't see the nodes you want please see the following article.

1 - Go to the Jobs tab
2 - Select the ROP on the left
3 - Double click on the drop-down list for the Machine Type
4 - Change the node by picking one from the drop-down list
5 - Click outside of the list field to complete the change