Set up a little spike test that overrides the matrix setup for the projection and model-view matrices to be identity values.  The test then uses visitor.find() to construct paths to all Rendering node-types in a scenegraph and sets up the matrices with a call to glLoadMatrix on my calculated matrices and then renders the Rendering node.  Other than the stuff to undo what OpenGLContext does automatically, there's no other matrix operations involved, the code could just as easily use a shader's uniform value instead of glLoadMatrix to get the MV matrix into the GL.

The paths automatically notice that there's a change in the scenegraph and update their matrices when they next render.  The rendering looks exactly as it did with the legacy code.  Still lots to do, but at least I know I haven't *totally* borked the math :) .