I purchased a used Craftsman LT 1000 17 hp 42"

I've had to do this at least 5 times. If you look under the body, there are two supports that carry the mower deck and lift and lower it. Each of these has a nut that holds up the deck and the nut is on a stud that goes up and down when you raise or lower the lever. Put the deck in the middle of it's range, around #3, make sure the key is off, move your blades so they are on the right and left edge of the deck.
Get yourself a device to measure blade to ground height, I have a block of wood that is 3 inches long. Make sure your floor or ground is level and tires are properly pumped up. Then raise or lower the adjustment nuts until both sides are equal height.

Gary