My apology to you if I came off a bit strong defending the KH 4 piston setup.
You are correct that the pistons can hang if if these cars sit outside for long periods, primarily due to pitting in the piston bores. These are so simple to rebuild and parts are not expensive.
As other members pointed out - the key is using the DOT 5 synthetic and using the car.
Also some vendors offer the stainless steel sleeving service which can be pricey but comes with a lifetime no rust guarantee.
These brakes work great as long as the cars are used.
The 73-76 setup also has some real advantages like low cost and increase in the bolt circle to 4.5" which allows for MANY more wheel choices.
The area I wish we could all get an alternative parts source for is the 10 x 1.75 " rear drums for the factory SBP 8.75" rear. Those drums are almost impossible if not impossible to locate new, and other alternatives cost $$$!