The visor on Rattrap certainly fits the character but as you mentioned, the air vehicle doesn't. What you could do is find more approriate mold body and cut and paste the head to see how it looks. The Botcon toy used Cybertron Ransack's mold which is already a spitting image of Rattrap.

Also I would suggest Air Razor to have Skyfall's body as the wings help to cement the character.

I taught myself to digibash by using the free paint application Gimp and this TFW guide for the method using layers.

I then followed these tutorials for learning to work with layers on Gimp:

http://www.youtube.com/watch?v=jrVnI3l9fgE

http://www.youtube.com/watch?v=ZaMdzX7-dVE

Hope that helps. I taught myself how to do it in an afternoon so its not too hard although it can me intimidating at first.