Aluminum vs cast iron cylinder head suspension effects

My 72 Duster with iron heads and water pump housing on the 440 was 3145 lbs. When we get it back over to the shop We will weigh it again.
The new torsion bars are heavier and we added subframe connectors . I just don't remember if the 3145 was before or after that work.
I figure a 3100 lb big block car isn't a bad recipe for performance. I am used to 4000lb B bodies and 4500lb C bodies so I hope it performs well in spite of the mild motor in there at the momemt.