Oz, most of us read, re-read, re-read, re-read, re-read, re-read, re-read, re-read, re-read, re-read, re-read, re-read, re-read, and re-read the rules to figure out what is and isn't required in which class, mixing between altered, modified, sidecar and whatever is as tough as it gets.
"Nothing is simple in the bike rules" (probably Jack)