TOPIC:

I'm trying to find a source for KZ400H LTD cables; will the regular KZ400 cables fit, or are they parts-specific?

I don't have any measurements, but the LTD cables might be a little longer [than the standard 400 cables]nbecause of the handlebar configuration.

Did you check part numbers on Partzilla.com?

Not sure what cables you need, but the clutch cable is the same as the 440 Ltd models.
So, as Nerdy said, some or all of your cables may be longer than the standard models.
If the handlebars have been swapped, then you'll have to figure out what lengths to get.

I'm probably going to need them all since the ones on the bike are pretty well rusted in their sheaths; I'm just trying to line up a cable source for them. It's probably going to be a while though since I have also snapped off an EZ-Out in the spark plug hole trying to get the remnants of some broken plug threads out - they just do Not want to come out. I had no idea the 1979 KZ400 LTD was so rare.   Are there any other crossover parts for the LTD from the regular KZ400? 

Whenever you need something, use the cross-reference at Partzilla. that would be a starting point.
There are some cases in which part numbers don't match but it may otherwise work. Matching part numbers almost guarantee fitment.
In a few rare cases the x-ref info is incorrect, but I've never run into that problem w my motorcycle.
Just don't buy anything until you're sure it will work. don't ask how I know. ha ha.

When you click on a specific part number below the diagram, another page will appear that includes a Fitment Chart showing all of the Kawasaki models that use that part. As for sources, it looks like aftermarket or taking a chance on some new old stock from fleabay. 
Motion Pro is a likely source.

www.partzilla.com/catalog/kawasaki/motor...1979/kz400-h1/cables

I suspect there are many shared parts amongst the various 440 models. To be sure, you can check the fitment charts for what you need.

www.partzilla.com/catalog/kawasaki/motorcycle/1979/kz400-h1