Careful with the information, I am 98% sure T that there is NOT a conversion mount for installing a V8 on the slant 6 k member in the 66 67 Coronet. Even all the way to 70 b body even.
You will need to use motor plates or swap the K member, to a v8 K.
they are pretty ubiquitous. I have had one for sale ($100)for about 6 swap meets