Just to summarize: If the lower receiver was ever in a rifle configuration, you can’t make it into a pistol. Find out from manufacturer, where you are buying from and/or a long call to the ATF. If it is a virgin lower, you can make a pistol out of it, then SBR it. And finally if you want to convert to a rifle you can do that. Just no bueno going from rifle to pistol. No FFL necessary if it’s same state and your state law allows firearm transfers between private parties without a FFL. Cannot ship unless going to a FFL, and you have to follow the guidelines on shipping a firearm.