I actually have that book (back home in Australia, I've not seen it for years!) and have referenced it many times in these chats. The team selected by Derriman was an attempt to statistically choose an all time Australian XI based on by how far players outperformed their contemporaries. Each player was assigned a batting and bowling rating (and all-rounder rating) and the qualifying criteria was 1,000 Test runs or 75 Test wickets.
I am going by memory here (so HookShot can correct me if I get any of this wrong), but Derriman said he based his selection on the old theory that an ideal XI consists of five batsmen (two openers and three middle-order players), five bowlers (two opening bowlers, a first change, and two spinners) and a wicketkeeper and so that is how his team shaped up. He acknowledged that it had a long tail and said that serious consideration was given to including Keith Miller who had the highest all-rounder rating. However, he said that if Miller went in then Lillee had to come out, as both Spofforth and Davo had better bowling ratings. So, as he didn't want to lose Lillee he kept the team as it was. Bradman was named captain, and Miller chosen as 12th man.
There were several other "guest" teams named in addition to the ones noted above by HookShot, and it was interesting that Bradman, O'Reilly and Tallon were the only players who were chosen in every single team.