I like the tractor blocks. I would make them 9 inch blocks so no one will notice the slight addition in height to the bottom of the block. IF you wanted to add a different block, I would make sure that it was a hay wagon or a combine or a disc or a plow or something similar. I agree that a little boy is not going to be looking at pinwheels as a windmill unles you actually make a windmill. You are very creative so you will figure it out. IT WILL LOOK GREAT!