That was aimed at Kawboy, but I'll tale a stab.
The KZ1300 uses specific valves (not shared with any other bike or engine that I know of). The only valves I know of available are left over OEM ones and remaining stock of Versah Intake valves. MCG (and probably others) have "Reproduction" valves that could be left over Versah stock, left over something else, or ones they are having made by a supplier.
To the best of my knowledge these valves are all stock dimensions and are not available without the retainer grove.
When folks talk about "Over-sized" valves, they are generally talking about the head being over-sized - with the intent of increased performance.
Getting valves without the retainer grove would be problematic because the intent of the grove is to locate the spring retainer. Moving that grove up/down would change spring preload and coil bind height (same as shimming or cutting the spring pocket). But it would not change the clearance at the camshaft/bucket.
You have to grind the valve tip to increase that clearance and doing that you have to be careful not to grind through the hardened surface.
A note on that grinding.... While the KZ manual details how much you are allowed to grind off, if you have aftermarket valves, they may be hardened to a different depth. So that Kawi provided number is simply a wild ass guess on anything other than Kawi valves.
Getting "custom" valves made is not really that big a deal. Someone like Kibblewhite already makes Z900 valves which are very close. These LIST for $30/each. There is a good chance that someone could get a dealer license and have a dozen sets made for round about $20-25/valve.
The Z900 exhaust valves are 0.5mm larger OD head, 3mm shorter in overall length
The Z900 intake valves are 1.5mm larger OD head, 2.62mm longer in overall length
Stem size is the same
Retainer grove is the same shape
Would need to check Tulip and tip to grove length
