Regarding price and crossing between 3200/4200 have a look on the Eurospares web site.
There is a cross over, so it appears 3200/early 4200 share springs, and the pricing does vary, some are £25 each, some are £225 each!
Best to go to your main dealer with your spares number (on VIN plate), my experience is that the main dealers can discount to Eurospares prices or even beat them, certainly JCT600 Leeds are more than happy too as apparently they used to supply Eurospares!!!