I do not know. I would think it depends upon the type of Cobra you want to buy and whether or not it was previously registered and or if it was titled. You know how screwed up this state is.
Look at the RMV web site
http://www.mass.gov/rmv/regs/index.htm
My Superformance Cobra has a "Statement of Origin" with a VIN # so I assume that is what the first owner used to get the title. Then its real easy to insure and register with a title. Mine is registered, titled and insured as a 65 Ford Cobra Coupe.
Do you intend to build one? If so, which ones are you interested in?