According to the brochure you posted, you need to know the shaft configuration you want then add the weights together; without knowing the configuration you are looking at, no one is going to be able to tell you if the 40 or the 60 would be the better choice.
I've never heard of aerating to get rid of humps in a lawn; I would think that would be a separate effort, bringing in sand and compost to fill holes, or just dirt and seed the patches.
I've never heard of aerating to get rid of humps in a lawn; I would think that would be a separate effort, bringing in sand and compost to fill holes, or just dirt and seed the patches.