Upgrading a KZ400 engine with 440 cylinders and oversize pistons

There was no need to cut exhaust valve reliefs, there is plenty of it. As for advancing the cam. You will need a slotted sprocket or the quick and cheap way of advancing the cam 1 tooth. But remember the KZ400/440 rotates backwards. By advancing the cam exhaust valve clearance increases. 

I cut the valve reliefs because the 400 has some fairly large ones, and the original 440 pistons had nice divots in them where they hit the exhaust valves. Maybe that was from a loose timing chain or some other failure but I'd rather have clearance and not need it then find out the hard way. It's good there is plenty of clearance but the milled head and no base gasket brought the valves ~1mm closer to the pistons. If the reliefs aren't necessary that's great. If the valves need a little more clearance then it's there. Looking at it during mock-up and after final assembly showed good clearance either way.
I decided to set the cam timing to factory for now. The cam gear from a 650 has a few different mounting points and a couple of them would give me the slight advance that I want. I was going to use one of those but it uses a different timing chain. So in the future I'll either find/fabricate a slotted cam gear like Nebr_Rex said or find OEM parts that will work. 
New Vesrah heavy duty clutch springs should be arriving today. The engine from the '74 has a "new" clutch pack so I'll probably use that with the new springs on this. Once I install that and put the covers back on I can begin swapping this engine into the 74. 
I found a dynamo cover from a 78 KZ400 that has the all caps logo and matches the later bolt pattern. Should look nice after it's cleaned up. I like the all caps KAWASAKI logo a lot more than the later one and it looks like this was 78 only. 
 

100% agree with you on the logo. Being a Kawasaki fan can be hard sometimes because the branding is just so Monster energy neon green. They’ve made so many great bikes beyond the Ninja series (no shade on the Ninjas, they’re great too!), and the heritage and pedigree of their bikes is historically significant. I wish they would recognize and embrace all of those variances more, and give us “old school” Kawasaki fans a little more fanfare.