In Mass you would have to start with some parts of a street bike, but there is nothing that says how much of whatever bike you are using.
You have to realize that both of the conversions I posted are results of what the owner wanted. If they had wanted the bikes to look more like an original off road three wheeler then they could have just as easily done that. There is nothing that says either of those bikes has to have the CB750 motor or the XL650 motor. They could have used a 350X or a 250R motor had that been their preference.
In short yes, you could make a street legal off road looking trike and have it registered for street use here in Mass. The two examples I posted show that, even though their respective builds are not what you would consider an original off road three wheeler. It could very well be done that way though.
There is a member on here who had a street registered Tri-Z in Florida. I couldn't find the link for that one though.
85 Tri-Zinger 60
85 ATC250SX
86 ATC250SX
87 ATC250SX
02 XR650L conversion
84 ATC 480R