Not to disagree with DBD but I have had good luck with a little bigger cam in a 406. This one:
http://www.summitracing.com/parts/cc...39-3/overview/
You should upgrade the springs and check retainer to seal clearance. The Vortec heads we used did not require any machine work for clearance. There is more info on that build in my thread titled "400/406 Builds"