I would highly recommend starting to get familiar with the aircraft editor. I have, for many planes over the years, been very successful in modifying an existing to match a current model. Find one (native or from swap pages) that is as close to size and configuration as you can. Start measuring your model, and transferring the dimensions to a copy of your base using the editor. It can take a bit when you get started to become familiar with the coordinate system. Some items may take a little bit of guesstimating, but if your starting model is pretty close to begin, they won't have a huge impact. Weights will be the hardest - I guess there, and then adjust with an overall adjustment to get to the all up weight desired. Flight test to find the best CG point.
Scale the visual model to match the new physics model you have created. No, you won't be able to visually change shapes of anything, but the physics (how it flies) will be very, very close. Search here for how to edit color schemes, if you want to duplicate your models paint scheme.
Doing the above has always resulted in something that flies just like the "real" model. So much so, that if I have to adjust out a flight problem (CG, incidence, thrust, etc.), I can do it in RF first, and then be confident that making the exact same mod to the "real" one will work also.