Acoording to countyimports.com, these two bikes are the same thing except the rear fender. I can tell the gas tank is a little different too and the seat, but I think they are the same thing underneath.

The bobber has the same dimensions too. (70 inch wheebase and 26 inch seat height). I am confused why the choppers are called 3/4 size and the bobber is called full size due to these dimensions if they are accurate. The bobber does look bigger in the videos with people riding it though.