So I had a 2003 Discovery and it went the way of the disco and I wound up having to sell it for scrap. Good news is that it had a pretty nice rack and ladder that I was able to alter to fit my Defender.
It is quite sturdy. I climbed up on and tried to flex it. Discos are dying off and racks are cheap. It took me a day to convert it. The disco rack is wider and longer. I could probably do another one in a couple of hours. I didn't think to post progress pictures.