Took the whiny single tone horn of the Spark and replaced it with a Silverado dual tone horn. The part number for the Silverado horn is 23494624 and it is "plug and play". However, because the Silverado horn is two units (low tone and high tone) VS the original single one, some bending and rearranging was needed for the items to fit. I ended up fabricating a new support for the two horns, but with some bending even the original brackets could be reused.
I was too excited and didn't take pictures for a step-to-step guide, but make sure that horn openings are facing downwards.