The stock Harmon Rocket II does use a RV4 tail. Some of the fuselage and wing parts are from an RV4. You purchase the remaining parts and finishing kit from John Harmon. I used a RV8 tail on my two HRIIs.
Mark Fredrick offers a quick build F1, from Team Rocket, and it comes with a dedicated tail. There are no RV parts in a F1 kit. Currently there are two variations of wings, the sport wing and the EVO, which is a tapered wing.