Welcome, Kevin. I had a 1920J which is a 61". The JD is a 74". 1924, and earlier are my favorite Harley-Davidsons. Everything after that is modern. The following link is to Motion Machine Inc. who specialize in boring and honing J, and JD blind bore cylinders. https://www.youtube.com/watch?v=cDfueUhbGqs

This was my '20J. Sort of a piece of ***** but I liked it when it ran. I have a 1916 J now.