Hi King Rat,
thank you. Sorry for my "german-english". Yes, I mean lowering the front. No, it does mean the following.
Basically the springs do suit. If the 510 is sitting, there is no problem. A problem will arise, when the wheels looses the ground. In this case, the spring will jump out of the plates, because there is no basic tension, even because the spring is too short for this.
The solution: Shorter shocks. This could be for ex a Koni with a rebound, or a Datsun 280ZX shock with a shorter stroke. Now I hope, there is a shock in the market, which is around 4 centimetres shorter when it will max. drawn out. As I now so far, there is a Gabriel shock, that has a stroke which is arround 2,5 centimetres shorter than the standard shock of my Datsun 510.
Yes, it will be possible to make a rebound in the koni shocks, and I can use these really short and hard Nismo competition shocks in my standard 510 struts. But it costs much money. Better would be: Sport shocks for Datsun 280ZX which I could use without manipulating them.
Greetings from Germany (near Stuttgart, or simply "Mercedes City")