I know of a couple trails WAY out in western MA that are still legal...I'm from Pittsfield. They're all old roads that are no longer taken care of and have fallen into disrepair.
You could also hit Savoy State Forrest. If you hit the northern end of it, it gets WET and LOTS of washouts. Since its a state forrest, and the trails are old ones to different camp sites, they're still the roads, and not the ATV trails....you just need to look hard and maybe mark them on GPS. The Pittsfield State forsest is the same way...you just need to search. I stumbled across one or 2 in PSF, but I don't have a GPS and I can't find them again.
You just need to make sure you don't do anything stupid or stumble onto any ATV trails. (Most are marked pretty well. You'll see a little pic of a jeep with no top or windshield with the infamous red circle with a slash across it.
The BEST thing to do is go the state's OWN site...
State Parks Trail Maps
Then, print them out and carry with you if/when you are traveling in that state forest (or park.. but the parks are much more civilized and most do not have any roads that require 4x4).
Here is the key fact:
We, as responsible 4WD enthusiasts, are allowed on ROADS.. NOT trails.
If the map shows a multi-use trail but it has "road" in its name and it is not gated, we are technically allowed on them (as long you are driving a registered and insured vehicle). However, if the key shows it to be a non motorized/hiking trail with a road name, we are NOT allowed.
Also, you need to check both winter and summer maps if available, as the winter use probably includes snowmobiles on many roads and during the winter, those roads are NOT open to our use.. Ya hafta give the sled guys their time in the woods too.. afterall, they may only get 2-3 months to really enjoy their sport.
Yes, this can be a little confusing, but in MA, there are some roads out there that may require 4WD in some spot.. there are probably only 2-3 that would require it for most of the length.
Also, also, you do need to know where you are, as the EPOs won't necessarily accept the "I didn't know where I was" excuse.
Have fun out there and be good... if you are rolling along in low gear and come across some garbage that some hikers left along the roadside, because they couldn't be bothered to pack it out with them, stop and pick it up... and then, as you leave, stop by the HQ and put it all in the trash receptacles... so the Rangers can see you doing good.