Ti Shock spring will save 2 pounds but it's not really worth the bucks. The 426 has gone a long way in weight savings since it became the 08 450. Yamaha has removed weight from the frame, springs, pegs, clamps, bars, engine and hubs.
If you try to duplicate all that you would be better off with a new bike.
Most all the trick parts are gone for that bike. Carbon fiber airboxes, Ti subframe, magnesium hubs and clamps. Ti bolt kits, Ti footpegs, carbon fiber guards.
But you can get stuff like the front CR brake cable and guards from LightSpeedPerf . Tons of carbon fiber there also.
You know best money spent on the bike is the CR front brake route and yz450f exhaust cam in the motor. Then take off the manual decompression system.