Rear Spring interchange 3500 1 ton?
 

I am looking to upgrade my stock rear springs on my 03 K3500 crewcab. I currently have 6/2 (6 standard, 2 overloads), but have seen 6/4 on some little later trucks.

My questions are

1) Are the 6/4's heavier GVW wise than my 6/2's?

2) Are the later 6/4's the same length as my current 6/2's?

Thanks in advance, Eric