First up, I’ve been talking to Steve Law at Speedshack and apparently I need sleeve nuts, rather than longer studs and new nuts, so we’re just sorting out the right size 
So that it didn’t become one of those jobs I kept meaning to do, I’ve jacked the back up to remove the spring pads – given that nobody had a good word to say about them (not even “ooh, nice colour”) 
For completeness, I thought I’d show an exploded view of how the bits fit together …
The tapered washer A fits over a stud on the top of the lowering block B and locates into a corresponding hole in the bracket on the axle. The remaining parts are then bolted up through a hole in the leaf spring (represented here by the pencil). The 22.5mm washer D locates the top of the spring into the cast hole on the bottom of the lowering block, whilst the 24mm washer E locates the underside of the spring into a hole in the spring plate. What this means (assuming I’m right) is that once everything’s in place the axle cannot move forwards or backwards under load, relative to the spring, so any movement must therefore come through flexing of the spring itself.
Getting everything to line up is a bit of a fiddle, but with a bit of wiggling, pulling and pushing everything finally clunks into place and you can do the nuts back up on the u-bolts 
Speaking of u-bolts, is there any reason I shouldn’t trim the ends off the new ones, given that they’re sticking out ridiculously far down underneath the car … waiting to ensnare unfortunate rabbits that momentarily think they’ve cheated death by missing the wheels before having their heads ripped off by the u-bolts? 
EDIT 07/01/08 :
Dave : Trim the u-bolts
Always best to do it with the nuts on (as yours obviously are).
That way if the hacksaw spoils the threads, removing the nut restores the thread.
Shame about those pads Stu, they were a nice colour. 