Certainly should be easy enough for you to do it yourself Lily, but if not I can always post pics of either my Harris rearsets of the DP ones, both are fitted to bikes so all should become clear.
One thing to watch if they are 2nd hand is the 6mm rose joint bearings, make sure they move freely. Earlier this year at Castle Combe with a few of the Hants members of the DSC as spectators I suffered the embaresment of stalling the bike on the grid as the lights changed as what I thought was first turned out to be 2nd, problem was traced to a seized rose joint making 1st gear very hard to select, obviously if your going to use a reverse pattern shift this will not be a problem.