Thanks for the response. It appears that Australia was a destination for some of the Yallop's, i.e. Graham Yallop of cricket fame.
I have been in touch with author David Yallop of London who's ancestors also hail from the Norfolk area. He mentioned another English author, one George Hollyman, who apparently published a limited edition book on the Yallop's of Norfolk. I am in the process of trying to obtain a copy.