I have access to a 20 ton press to do my bushes but it is 20 miles from home, as long as I don't need my land rover for a day or so, would it be OK to remove both radius arms and possibily the panard rod in one go or should I just remove,(and then re-fit) one item at a time?

So long as you dont have to move your Landy once the radius arms are off then do them both at the same time.
The Panhard rod can also be done whilst you are doing the arms.
I'd be inclined to mark them up left and right but I dont think they are "handed".
I also cleaned mine up and repainted them whilst I had them off.