We recommend using the HB6C-3/8. You will most likely look at the HB6C-3/8 and realize that it is does not match up with the original tuning machines. The Rickenbacker headstock is a 2+2 configuration, if you were to install the correct looking tuner (BT1), there would not be enough room for your extender to swing(it will run into the G string tuning machine). The HB6C-3/8 will fit the headstock hole and mounts with one mounting screw. In the future, if you would like to sell your instrument, the existing tuner will cover up the new mounting hole that you have drilled.