Since any aluminum head is going to be better then a pair of cast iron GT40's you only need to look for ones with smaller port volume and smaller valves then some other aftermarket head. A set of AL heads with 2.02 intakes and 205CC port volume will produce less torque at low RPM's then a head with 1.9 intake and a 185CC port volume all else being equal. That's not to say that you can't build an engine with the big valves and not make the same or more torque then the smaller valve head you just would use a different cam, compression, or intake.