in {TAIL ~ step} each of the second cooktop units is preassembled with {HEAD ~ a respective single cooking system type} prior to mounting on the base units, and 
in { TAIL ~ step } each of the second cooktop units is preassembled with { HEAD ~ a respective single cooking system type } prior to mounting on the base units , and
OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH