Will an 86 ATC 250R bearing carrier fit an 85 swingarm?

[BIGKAHUNA]

Is there any advantages in using the 86 swingarm over the 85?

No, the bearing carriers and swingarms are different. The swingarms are interchangable. You can use an 85 or 86 swingarm on either, but you'll also have to use most of the assories. That includes the rear brake set-up too.

The advantages, not many, the 86 is lighter and may be easer to adjust the chain. I can't see much more.