I've never seen a Jupiter in person but from the picture it looks like a straight wing (no sweep) so it doesn't really matter where you measure the CG from along the wing. It will be physically easiest right next to the fuselage as suggested by Red Head. Most of the members seem to agree that low wing planes should be balanced inverted (unless the manual says otherwise) and I have a hunch the manual has little to say about this either. I usually just put a piece of tape on the wing in the approx correct area. Measure and mark the tape with the correct point and then suspend the plane on the balancing points. Balance by moving receiver and/or battery as first options before adding additional weights.
I also agree on the 85mm. A tail heavy plane can be a real hand full to fly.

Good luck.