I am building up my truck using an 85 pickup cab and bed, on a 86 4-runner frame. As far as I knew the only body mount i know that re different were the third set back, they need to be cut and moved back 5 3/4" to adapt the 85 cab. I was positive that th front mounts and the second set were the exact same. If they are not, i am in for a nice suprise.
plus you have to either stick with th carbed 84 motor or swap the harness over from the 4-runner which is a huge pain.
Ultimately I would say solid axle the runner, much easier.
My shirts all F'ed up 
i don't think you understand, they are both 4runners and i will be useing the 86 body and 86 motor wich were both together to begin with.
