I've got them to scale, but I'm trying to line up a sprite for a treasure chest on top of the model (going for a retro look) but it just tiles the sprite all across the model.

Is there a way to position the texture on the model or is scaling the only option?

There's no way to position a texture, all textures have to be seamless repeating patterns. The UV mapping is based on the world position of a block and doesn't take into account any local values for the block.