Oh to be a boy again, the things I would do differently........

Thin foam from a meat tray or similar grocery item works nicely for CG location purposes. Like Rotaryphile I have done the small glider thing for a lot of airplanes and it has been fairly accurate, certainly enough for test flights to be made without crashing.

The last one I did was a 4 inch span IFO model because I had rebuilt the larger one (not much to do on that model) and forgot to write it down anywhere.

If I remember right the Simitar is a flying wing design by Evans. It should work OK with that. The bigger the glider the better though.

For a really odd planform of any sort, take a planform picture with a digital camera, print it, copy that to the thin foam, and proceed with glide tests.