I've actually ported some Clojure code to Common Lisp no later than two weeks ago and it was pretty much as straightforward (if not more) as porting R5RS to CL. In my (admittedly limited) experience both CL and Clojure favor a certain high-level coding style with complicated macros versus the more simplistic style of Scheme. Contrast CL's loop construct, Clojure's for statement and Scheme's typically more recursive approach to iteration.

You're welcome to draw the line wherever you want, maybe for you conses are mandatory in a Lisp language but I don't really understand what you hope to gain from this discussion. I might as well say "tail call optimization is absolutely mandatory in any self-respecting Lisp, therefore CL isn't a proper Lisp dialect".

This is effectively the same level of discussion as a Java programmer saying that C++ isn't "true OOP" or an Haskell enthusiast claiming that Scheme isn't a true functional language because it allows side-effects. It's just silly gatekeeping that doesn't lead anywhere interesting.