Two questions: 1. Are the forks even with the top clamp? 2. Have you made any adjustments to the rear shock (rear sag, rebound, compression, etc)? 3. What is the condition of your steering stem bearings (lubed and free moving, especially the lower bearing)?
The reason I ask is if the forks are even with the top clamp and reducing sag should help tame down the head shake. Also, if the lower bearing is frozen, rusted up, it can affect the head shake as well. I would suggest making only one change at a time, forks first, to see what had the most effect.