No, classic trucks on a skateboard will not work for longboards. Longboard trucks have a much wider truck base than usual trick skateboards. I've ridden one a few times and they are much easier to ride than classic boards. Fun as well.

I recommend just buying a complete board. It would be cheaper than buying the parts seperate, and longboards are just for cruising, so high quality part, in my opinion, are not needed.

I know here in Canada, complete longboards go for about $250. That's what I would recommend.