what rear axles (year) would fit on an 84 4runner

 

Anything from 84 - 85 truck or 4Runner should work. 86 and up wont work because they made the rear ends wider, so the axles would be to long.

 

79-85 will fit if you are looking to just replace the axle itself or the entire housing
swapping the complete housing from an 86-95 does gain you 1.5" in width on each side and bigger rear brakes, early brake drum on the left, later IFS rear end drum on the right, bigger brake = better

you would just need to run 1.5" wheel spacers upfront to get your track width to match.
very common swap

 

I found an 87 im going to need wheel spacers correct?

 

Not required, you can leave the front as it is and the rear will be 3" wider. Or you can add the spacers up front if you want the f/r track to be equal. I ran almost 10 years with a narrower rear axle than my front.