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