For a start the double valve springs should help eliminate valve bounce at high revs.

I have a 1200 ute which runs an a15, 60thou oversize pistons, shaved head, ported+polished and running twin 40 dellorto's. I also have transister ignition. I don't have double valve springs. Could someone please explain how they work and give me some feedback as to whether they would be suited to general hooning. I have also considered larger valves, i am interested in which valves to use, the cost vs performance increase etc and if my reliability will be compromised.