KH piston dust seal fixable?

There's really nothing wrong with the calipers that you currently have, it's just the early design of the way the dust boot is attached in the bore of the caliper body itself.
In 67 to 72 the most common design was used, as most likely it cost a lot less in the manufacturing, machining, process to get the calipers made.

I got to thinking about this, and hope you wouldn't have to purchase whats knows as "A master rebuild kit" to get those parts that you need.

Not to toot my own horn here, or anything to detract from your posting, but i will soon to have a rebuilt pair of KH brakes ready for resale, when the replacement pistons get here thru the FEDEX people.
Keep an eye in the for sale section.
Jim V.
hemi71x