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I picked up a 79 KZ400 today. Not running, but does have 160psi compression on both cylinders and spark. It has been 4 years since it last ran.
 In the service manual section has a manual for 74 - 77 KZ400. Is this close enough?

I do not know off hand what if any differences there are between 79 and 77 models there is.  So can not say if the earlier one will be enough or not.  But will say there is another manual at this location for the 78 through the 81 model years. It has been broken into several different pdf files, so if you want all of it you would have to pull each one down. You can find it here 
kz400.com/WorkshopManFrameset-5.html