What tool are you using to turn the preload nut? I don't recall Guzzi including a spanner wrench with my bike and I don't have one lying around. I assume the first thing to do for preload is to turn it all the way to soft and then start counting full turns until you meet 13 or whatever your final setting might be?
Same with the rebound screw? Turn it all the way counter clockwise and then start counting clicks as you turn it clockwise?
Same with the rebound screw? Turn it all the way counter clockwise and then start counting clicks as you turn it clockwise?