Dave,
Yes, the axle is moved back when current style springs are fitted. Mulfab quote 15mm. If you study current pictures of cars in build you will see an offset from the rear face of the shock absorber hoop to the forward most washer on the top shock absorber mount, this spacer is missing on early hoops.
As to the reduction in distance between the top and bottom shock absorber mounting points. This for two reasons, the overall depth of the leaf itself, 4 leaves compared to 6 - and - the nice new springs are a damn sight softer, so the car sits down and flattens the spring and reduces the space the shock absorber can compress in. So much so that when combined I found I didn't need lowering blocks at the rear to match shorter front springs.
