The question is: Which state?
While it is really easy in some states (and some states don't even issue a title for bikes), other states can be a real problem. Here in Tennessee you can title the bike to the engine. So, you buy an engine with legible # and a bill of sale, build a frame, and off you go to the DMV. Or you go to a car dealership and have them verify the VIN. May cost a few bucks, but hey!
Ths may and does vary from state to state. On top of that some states may not accept a build title from another state, so even the title is no guaranty
Ask the (Hot Rod) guys in the People's Republic of California...