The weakest area of any '73~'80 Kz900/1000 is the steering stem head area and the top frame tubes. You can clamp a stock unbraced Kz frame in a vice, put a 4 foot tube into the steering head, then push on the 4 foot tube, and watch the top frame tubes bow outward!!! All that stock tin plate gussketing below the steering stem is worthless. Cut all that away and replace it with some tubing as in the two photos below. Then toward the rear of the top frame rail make up some triangular bracing that tie those three frame tubes together. You can do it with tubing, or with flat plate welded together to foam that brace. You can see what I am talking about in photo below. All this will keep the steering stem area from flexing. Then you could tie the rear of the main frame hoop together as in the photos enclosed. Then throw away all the stock motor mount plates and bolts, and go with oversized bolts that you have to tap into place on the frame and motor mounting areas. I went with American bolts on my bike, and used an adjustable ream to open up my frame and motor. Make up some thicker motor mount plates as in photo below. This ties the motor to the frame making the motor part of the frame. I have seen many a Kz front motor mount areas where the frame left marks from the frame moving around the motor!!!
Remove all that worthless tin plate gussketiing under steering stem head and replace with tubing.
The triangular brace tying the three top frame tubes together.
This bracing ties the main frame hoop, swing arm pivot area to the steering stem head.
These are the oversize motor mount plates with ream fit motor mount bolts.