Ended up going a totally different route.
Drop Spreader wouldn't work (thanks for the confirmation) and top dressers are too expensive (dropping $5,000 on one piece of equipment when my annual income is around the same amount is a ridiculous idea no matter how big I hope to grow in the future).
I purchased the Earthway 2130 spreader (
www.rittenhouse.ca/asp/Product.asp?PG=2135). It was totally different than I was thinking, but looks like it will work perfectly for the right price. I'll find out!