On a level concrete or blacktop pad, get it on jack stands with the wheels and tires off and the chassis level.
Pick 4 points on the chassis on each corner(swing arm pivots/spring mount/etc) and mark, then notate in a log book. Drop a plum bob off each of these points and mark an 'X' on a section of tape stuck to the floor/pad where the plumb touches. This need to be very accurate ! Measure front to rear, left to right, and diagonally on both sides. Notate in your log book. This action is called 'squaring the chassis'. From these measurements you can determine if the chassis is out of square.
Next drop your plumb bob off of the center of each wheel hub and mark on tape on the floor. Measure once again side to side, left to right, front to rear, and diagonally. Notate in log book.
Now take measurements from your wheel hub center marks to the 'chassis' marks to determine if the suspension is squared with the chassis.