Hi Simon.
I also started the fitment of my RHD RCR dash in Australia. I also found the gap to the front window to be quite a lot. I ended up doing a bit of a dash comparison and the RCR RHD and LHD ones are very different (see
http://claw.com.au/gt40_interior.html ). I swapped mine out for a different one but you should be able to add some material to it to get it closer to the base of the windscreen. I will post some images of my RHD dash possibly this weekend. I have had to correct its finish near the base of the windscreen/spider as well.