I would have to recommend an engineer for your area. Knowing how strict Mass is on everything
I would go for an engineer due to the many questions which will come up. A contractor may do, if they are really good, and they have references where they have done this many times before.
Finding an architectural company or Remodeling company that has an engineer in the office is also a good way to go, but the bottom line is, they have to hire an engineer.