My younger brother bought my 86 trx250r. He can get an 85 ATC 250r swing arm and bearing carrier for $40 but hasn't looked at it yet. He wants a shorter swing arm and I would like to know what size it is compred to the stock 86

 

It is the same length, unfortunately the brake setup is different and won't work without swapping out hardware.

I believe a 400EX swingarm will work, it is 1.5" shorter and weighs about 1/2 of the steel 250R unit. I would look into this as an option.