Howdy.
My brother uses a Stellarvue ED80 as a guide scope and an Orion guide camera, the one they released recently, to which he found that an extension tube was necessary to get focus. Try getting some cheap PVC pipe to do an experimental duct tape rig up to see how it will pan out and may also give you an idea of the length of tube you need to have made.
Definitely ditch the Barlow, you're reducing your field and options heavily. Is your guide scope in rings with adjusting screws so you can line it up where you want it better. Its not a bad idea. Good luck!
