Are you referring to the stainless steel sleeves for the piston bores?
If you are, a friend installed the K-H calipers with stainless steel bore inserts on his 1970 Duster 340 5 years ago, and they work perfectly.
Basically the stainless steel bores solve the issue of the pitting of the bores, common on cars that sit for long periods without being driven.
I plan to upgrade to stainless steel bore calipers on my 1971 Duster 340.