I looking to add dirt bars to my cbr. Rather than drill holes in my top clamp, I thought I would raid a salvage yard. To do this, is the fork diameter the only consideration? Do I have to consider rake or any other factors?

 

If you're looking for the same model and year from a salvage yard, then you don't have to consider anything. I'd go online to a parts site and look up your part and then see what other models it fits. If you're going to try to use something from another bike, then it's not just fork tube diameter you have to think about. Distance between the fork tubes, the amount of fork tube offset and steering stem diameter just to name a few.