I would like to add to Vurtok's theory....

The 69-70 smog head does work good for Torque apps.... so does the heavy head up till 74'....

What makes the torque is the small runner design...170cc intake
when you use a bigger runner size you can make more torque but at a higher rpm range...this isn't good for a heavy vehicle...

They heavier the vehicle the more conservative you should be on the runner size.....

The vortec have a small runner and what make them really shine above others is the swirl finished combustion chambers...they are 10 times more efficient than the heads of yesteryear....

As far as the aluminum head issue I agree and disagree.... they do corrode faster but as far as the sealing co-efficient I would not worry about that.....The big 3 has been producing aluminum headed motors for 20 years or better and head gasket problems are a thing of the past.....