Complex sentence: He placed a knob marked "Tone" on the volume-control spot, then using a vinyl record he carved into a pick guard to cover the controls; this pick guard was later replaced by a real, similarly-shaped pick guard.
Split into simpler sentences: He placed a knob marked "Tone" on the volume-control spot, then used a vinyl record that he'd shaped into a pick guard to cover the controls. This pick guard was later replaced by a real, similarly-shaped pick guard.