Hi, Series 1 auto manifolds were smaller bore, the larger bore came in with the series 2 manuals. the auto and manual downpipes were different, the auto joining together by the bellhousing and manual's at the rear of the gearbox. The downpipe and system is no guarantee of size because I have modified different systems to fit on the 'wrong' manifolds and so may others. Any differences of manifolds left to right would have been due to the fitting of an AED on the early cars, later ones are the same side to side. P5b manifolds are different side to side and not interchangeable. Range Rover manifolds although similar the left hand one is peculiar to the vehicle. Perhaps Harvey can elaborate further with any more info.
Colin