Personally, I think GroupLayout is pretty nasty so I don't recommend it in any case (pretty much write-only and very fragile). SWT GridLayout is far superior for SWT/RCP work and can do pretty much anything you could ever want.
Yes, now I see that they are available. I was missing a special instantiations class. I also filed 2 problems in the bug tracker: They have to do with WB and classloader not going through every attached jar in the project to find required classes. The second one is with a property editor now opening and throwing a null pointer exception.