I have converted lots of RC models to CL scale, using these general rules all of them have flown great...I even converted the 1/4 scale Bravo kit from Sig.
I have seen a Gee Bee fly CL before, it can work.
Here is what I would do.
1) they are right, attach the bellcrank to solid structure that can take up to 50 lbs of pull.
2) put an adjustable line guide on the model, the position of the line guiide relative to the CG determines the line tension. The Bellcrank can be almost anywhere. I generally put the bolt for the Bellcrank 1" behind the CG
3) 1 or 2 ounces of right wingtip weight would help, but I have flown some models without right wing tip weight.
4) make the tailwheel adjustable, but fixed, the position of the tailwheel is critical to getting a good taxi
5) I would highly recommend throttle control for the model, a model that big would be scary if the engine was stuck at full power with no throttle. I have a PDF copy of my book that talks about the electronics used to control the throttle. Or you can install a 3-line system which will cost alsmot as much as the single channel system that I use.
6) I would start with the CG at 25% and go from there.
When you fly it, hold full up elevator and throttle up slowly, nose may pitch over if you throttle up too quickly....it would look great.
check out this web site, there some large CL scale models on this web site that can show what is possible....you can get a copy of my CL scale book (PDF copy) from this web site.
http://www.eicnetwork.com/eic/Home/Home.html
Land softly