Here is what worked best: create a blank anchor para tag, set its attributes to 'top of left page', and insert *two* frames in it, the first locked and the second floating. Import the figure into both frames and position as required.
Using two separate anchor paras/frames, one for the left page and one for the right, works, but only if the two halves of the figure occupy the whole page height. If they do not, the space below the left-hand anchored frame remains free of text (obviously). -- Steve
