****HIGH QUALITY & PRECISION (unfortunately my car is a prototype!)****
My 1967 Eldorado was the 25th Eldo made in 1966 and has several parts which are different from the "finalized" parts used on the next 17,000 Eldorados. Instead of using the two-piece shackle bushing inserts from Steele Rubber, this 25th Cadillac Eldorado used one very large steel-cased rubber bushing on the upper shackle and a slightly smaller steel-cased rubber bushing on the lower shackle, a twin size of the bushing on the front of the leaf spring.
Notably, the 1967-70 Eldorado's rear leaf suspension was criticized for creating a booming noise and slightly rough ride. In my prototype Eldorado the larger bushings have a softer ride without the "booming" noise.
Why Cadillac switched from the larger bushings to the two-piece insert bushings (like the ones from Steele Rubber) we will never know.
In 1971 Cadillac abandoned the Eldorado's rear leaf spring design for coil springs also with air-ride level control.
IN CONCLUSION although the Steele Rubber bushing inserts do not fit my VERY early production Eldorado it's my critical opinion is that they are of very high quality rubber and precisely made.