[LH Lead-Foot]

I agree rjs53, But that type of phenomenon would be caused by two different problems.
One is the wall thickness of the metal used in the driveshaft tube itself. When aluminum became popular (Reduced Weight for CAFE #'s), the outside diameter increase noticeably.

Two is the length of the tube, thus resulting in flexing. This problem can not be solved by balancing, but a shorter stiffer tube, properly balanced would correct that issue. From school busses, farm trucks to stretched limo's will require multiple drive shafts.

I would prefer to keep it simple. If there are no issues with a factory designed 2WD Tahoe 4DR driveshaft, shortened about 2 inches, worked fine for me. I was almost convinced that it would fit without having to be shorted, but didn't work out that way. Motor mounts, distance from radiator, bell housing bolt access, headers, etc. all created factor in the application.

I was concerned the crossmember would be an issue with the rear axle off the ground...hanging, but wasn't even close.

I have never seen welded weights on the front, always on the back.
But I would not be surprised to find some factory drive shaft with weights on the front & back also. Just never seen them while servicing a U-joint or pulling at trans or diff repair.

But I am not the engineer and the subject never come up while in Troy, MI.I am sure there is a limit to length that is always factored in, regardless of material.