Sorry, can't say for certain, but I doubt they're interchangeable. They're two different engines, the '82 650 is a SOHC, and the '85 is a DOHC. Even if the diameter is the same, the spacing and angle of the exhaust ports could easily be different.
You'll get more and quicker (and more informed) replies if you post questions like this in the "SOHC4 Bikes" forum. The Open forum is for all things non-sohc4 related.