Steve,
the principal difference is the location of the knife edge mounting, which is closer to the axle on a 400 front arm.
Fitting a standard arm on one side and a 400 arm on the other will result in noticeably softer front suspension on the side with the 400 arm.
There are other differences, such as the heavier duty droop stop bracket and larger wheel bearings on the 400 hubs, but these do not affect how the car handles.
ken
Steve H wrote:
Now the question,(Sorry for the long winded intro) Will the 400 arm fit a saloon and if not how can I identify a 400 arm from a saloon arm?
Many Thanks in advance Steve