Which one? There were three different ones that it followed in CT, RI and MA. I think the one via Springfield and Worcester would probably be the most feasible at present.
Back in 1991, I rode a train from somewhere in Mexico (Aguascalientes, I think) through Monterrey and up to Nuevo Laredo. This was the year before Mexico killed off ALL intercity rail passenger service. I was a spry 18 year old at the time and didn't even bother to pay attention to what I was experiencing. Before news of the total annihilation of the FerroMex passenger system, we were talking about chartering a train all the way from Longview, TX to Aguascalientes and/or San Louis Potosi. Proposals seemed to be optimistic and infinitely more comfortable than 24 hours of bus riding. But alas, it was never meant to be.
Since then, Nuevo Laredo has become even more dangerous to US Citizens as it is so close to many of the border drug traffic wars. So sad.