I got an email of Gwyn just this morning....
They will work with standard springs. If you plan on many road miles then he recommends the EMU or terrafirma shocks as they have stronger damping.
I can't provide much help, sorry. I would say though if you are going to start throwing money at it I'd buy an X brake.
I intend to.
I'm not sure even when they are sorted that they are entirely reliable. Mine sometimes fades terribly - and there is nothing wrong with it.
I bought some HD spring off ebay recently - they are colour coded and listed under the part numbers - but when they came were britpart items....
Ebay link
They were though £34 per pair.
I think the whole thing is a minefield and I think you could end up returning most of the springs that you got sent by most of the suppliers - perhaps the only way to guarantee LR parts is to buy them from LR?
For the price of yours though I think I'd return them.
I looked at those - but my side windows clear very well from the front vents... so hardly seems worth it.
I did wonder about the high flow window vents - but they are pretty expensive.