2wd Diff Balancer Questions

[Bala de Plata]

I was working on my brothers 4x tacoma today and he does not have a diff balancer. I ask you to confirm that this is the same (tacoma vs. 4runner). If 4x dont have them and dont need them, what makes the 2wd different? Is it that a 2wd is longer? I read the a write up on driveshafts that was posted on another thread discussing Cardin joints vs. CV's and it did not mention anything about a diff balancer. Probably cause the write up was mainly discussing 4x.

What are your thoughts?

Diff Balancer in question:
Metal ring

Rubber bushing meant to be sandwiched between the ring and axle.

 

[TechWrench]

I've never owned a 'Taco', but from your pics, those rings look to be too large to fit between the diff and the u-joint flange. Are you sure they weren't originally around the body of the drive shaft? It's hard to tell from the pics, but it looks like the main body of the drive shaft is larger than where the u-joint area. I have seen other vehicles that use bands around the center part of the drive shaft to dampen vibration, maybe that's where they came from!