Haynes Manuals have a reputation for being incomplete. This is no exception!
The Project Vehicle is a Series 2A, and there is little Series 3 in the book, not surprising as the original was written around 1985! Series 3s were still new then!(There IS a Series 1 section though.)
What it IS is a manual that covers, if not in great depth, some of the jobs no other manual covers. Such as Chassis repair, outriggers and the rear crossmember. Fitting new seatbelts, free wheel hubs, and the fairey overdrive. Replacing body panels.
This should be read in conjunction with the official Repair Operations Manual, and the Land-Rover Parts book for your particular vehicle.
Also, try joining the Club for your vehicle. Such as The Series Three Owners Club.