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