Nice! I also started on a KZ400 -- 1975 and blue/black/gold with the "ohc 400" on the side panel -- the first thing I did was tear it all apart because it had low compression and an oil leak thru the cylinder studs! It's super exciting to see what has changed (and some things that have not, like the steering head ball bearings!). Valve adjustments are a bit harder now (they used to be 10 minutes, thru the leaking cam covers!) -- but we did ours at 1k miles so my daughter could learn -- we just took the shims out, measured them, and put them back, then upgraded our clutch components to 2020 parts! Next we'll be replacing the coolant o-ring with a norton part out of an abundance of caution. The best thing since the old days is you can order all the oem parts right to your house!
Enjoy your new ride!