The OP asked about the Granite Rock locomotive. The last time I heard anything about it, and it's been a long time, was it was disassembled (to use the term rather loosely) with the intent of restoration, but upon close inspection, the project was then found to be prohibitively costly. This sort of thing happens when the boiler jacketing and lagging hasn't been removed from a locomotive destined for outdoor storage, and the weather at Logan, where the locomotive sat out side for several decades, is exposed to marine conditions because the jacketing and lagging can obscure serious boiler-related problems (see J. David Conrad's discussion on how to prepare a locomotive for static display in an outdoors setting). I also recall hearing that the frame and running gear were "completely shot".

The rest of the posts, particularly the ones castigating the CSRM, are "whyncha-ims" at their best (as in "whyncha do this, whyncha do that"). I notice that some of the biggest whynchas are the armchair/photographer railfan types, and as such are the least experienced on how to care for and warehouse such large objects as railroad equipment. FWIW, over the decades CSRM has looked into indoor storage for this stuff, and it has always come down to: prohibitive costs (as in buy property convenient to rail service, construct a yard, pay for a building, etc.). For a while before the Museum was opened, a lot of stuff was stored at/in a Safeway warehouse, but eventually Safeway threw the stuff out. It came down to using sections of the SP shops (where the roof of the Unit Shop let in more rain that it kept out), and they almost lost out on that as well (all developers want is money, and "nobody rides trains anymore").

If something has been built once, it can be done again (or restored). It all comes down to the question of cost. Look into the costs of fabricating a completely new locomotive. The British do it, so do some Americans. Then, if you have the money, bring it to CSRM. Otherwise, you're just a Nattering Nabob of Negativism.