Spark unit interchangability

So, I just picked up an 85 interceptor vf700 for 400 bucks. Its a bit rough, but now I'm just trying to make it run. I have narrowed down one of the problems down to a bad spark unit. I get fire on two cyl's, Switch the CDI's and the other two fire.
The spark plugs firing are still firing weak, which could be due to bad plugs and wires, but my question is,

Are the spark units interchangeable between models, vf500 vf750 ect.

Because on ebay, I haven't been able to find many 700 model CDI's ( inexpensive ones that is ) But there seems to be a slew of vf500 CDI's listed.

Thanks!

 

Also, I check the resistance on the pulse generators as well. One side is right at 480ohms, Which is what it is supposed to be, and the other is 496, Does that mean its out of limits? The book does not specify how far it can be out if at all, just says approx. 480 ohms.