You're actually better off to lay it on a piece of glass... like a glass table or window. Something you know is truely flat. Or a something that you can take a level to, to ensure its completely flat.
Also, stick the axle thru the swingarm and put a level on that once the swingarm itself is leveled. See if the axle holes are true. Also measurements from center of axle to the pivit bolt.
aka Gas Man
Was: 2002 Kaw ZX-9R
is me till the