I too had the dilemma of using a cut bushing, but after a pretty exhaustive search for 80-85 durometer rubber in blocks large enough, for a reasonable cost (I even looked in McMaster Carr and found raw material for several hundred). I was beat down and decided to use the easily obtainable, slit bushing that I could find oversized at the local store. With a total investment of $16 ($8 dollars a package with 2 ea, remember I said I had to make 4 to get 2 I was happy with)
When push came to shove I decided this was better than several other ideas I had, as I really want that factory rubber look. Truthfully the slit bushing can barely be seen on the bottom of the car sealed inside the metal housing. I really believe 99.99% of people will never know, care or even know whats truly correct, but I understand your hesitation as I too have traveled the path and had to be at peace with my decision prior to instal.