It shouldn't move that much

. Make sure the all the bolts on the back of the instrument cluster are nice and tight (don't go nuts though).
My guess would be to check the bolts & nuts holding the headlight / instument bracket to the frame. Try & see if the headlights move excessively up and down. If so, tighten these bolts/nuts. If they can't be tightened any further and the headlights still move heaps,the rubber bushes around these bolts probably have sightly perished. You may need to replace them or you could do what I ended up doing and that was to put an extra washer under the nuts to give you a little extra thread to allow it to be nipped up tighter.
Hope this may help.