I hiked over Allsop pass about 20 years ago from the opposite direction. It was very difficult coming down as it was so steep that we couldn't see the whole slope at once and hence couldn't pick out a route that went all the way to the bottom. We had to traverse back and forth across the ledges working our way down a little at a time. It was tough with external frame backpacks. From the direction you are going, you have the advantage of seeing the whole thing at once. Here's a picture of what I would try, but there is no guarantee of success. I think that the way we came down was significantly to the left of the arrow, but the gully the arrow is pointing to looks better to me.