Champion plugs seem fine in a car but I always found them pretty poor in any motorcycle. Not saying they are the cause of you problem but lets see what others have to say.
I dont know what ngk plugs are recommended for the kz1000 so cant say what the Champion equiv would be.
do you have a multimeter to check power to the coils? With ignition on and meter on DC volts put red probe on red wire at the coil an black probe to earth ie motor or frame.
Voltage should be close to or just s bit lower than that of the battery
What am I missing here. The first two photos show 4 plugs that that look very rich but none have the electrode and the earth strap bridged. Then in photos 3&4 you show a plug that is nothing like the first four. In forty plus years of being a backyard mechanic I have never seen a plug with the electrode bridged to the earth strap, let alone have that happen in a “couple of short rides”. Please show us the most recent set of plug and there condition.
NGK B8ES is the factory recommended plugs. Or Nippon Denso W24ES-U
Did you talk with Murray’s about your bike to get the jetting correct before purchase?
Think outside the box on jetting
Age and condition of valve guide seals (remember Smoking stated )
I experienced this condition
Original owner 78 1000 LTD
Mr Turbo Race Kit, MTC 1075 Turbo pistons by PitStop Performance , Falicon Ultra Lite Super Crank, APE everything. Les Holt @ PDM's Billet Goodies . Frame by Chuck Kurzawa @ Logghe Chassis . Deep sump 5qt oil pan. RIP Bill Hahn