Lubavitshe Rebbe suggesting Rabbeinu Tam Tefilin for Rav Moshe

Igros Moshe (OC IV #9)  A letter to the Lubavitcher Rebbe in response to his call to wear the teffillin of Rabbeinu Tam   When I was in Europe I had tefillin of Rabbeinu Tam that were exact to the smallest detail which I wore after the prayers. But I wore them without an oath that it was an obligatory custom.  Also when I came to America with the mercy of Heaven I wore them for many years when I found a good pair according to my views.  The issue is that there is a great difference between the teffillin of Rashi which are obligatory and should be done to the smallest detail which nonetheless must be worn if they are kosher even when not they are not made in the most exacting way. Therefore over time much has changed and there are not so many scribes that  are knowledgable how to make them properly nor even proper parchment. Consequently the mitzva of Rabbeinu Tam must be done with the teffillin that have been made in earlier generations. Even those that were made correctly to the smallest detail have deteriorated over time and it is questionable whether they are valid today. So the teffillin of Rabbeinu Tam since there is not an actual obligation not even a possible one, since we clearly have ruled for hundreds of years that the Rashi teffillin are the only obligatory ones and everyone has accepted this. Nevertheless since the teffillin of Rabbeinu Tam were worn initially in many places including the place of Rambam, it is desirable to try and fulfill the mitzva also according to Rabbeinu Tam. Even if Eliyahu comes and tells us to wear Rabbeinu Tam we would not be required to accept this. While other views about teffillin exist, it was only for a few pious individuals and is not relevant for us. In contrast Rabbeinu Tam was once a widespread practice and it is good to try and fulfill it also.  However since it is not even a possible obligation or local strictness, I would not wear them unless it is certain that the tefillin have been made properly to the smallest detail and thus have no uncertainty about their validity,  That is why I did not take them from Russia which was very difficult.  I was also forced to leave there many seforim and many of my writings. When I came to America I did not acquire Rabbeinu Tan tefillin from those that were available. However once I qas able to get an old pair of Rabbeinu Tam tefillin which were good and I wore them for many years until I needed to inter them. .In contrast I acquired the obligatory Rashi tefillin, I acquired twice , once fron Israel which were made accordibg to my instructions. But I did not make an effort to grt tefillin of Rabbeinu Tam since there is no actual obligation to wear them even as a custom. Even though my father wore them every day.  In addition they are vey expensive. I had put them on bli neder and thus since there was no obligation I made no effort to obtain another pair.  The issue is that since most of those who wear Rabbeinu Tam are chasidim, the sofrim who make them are also chasidim and since Chabad follows the Rav’a Shulchan Aruch the sofrim also follow its rulings and it conflicts with the rulings of the Shulchan Aruch as to how to write tefillin.  However you have informed me that you know an expert scribe that you offered to send to me who can write Rabbeini Tam tefillin according to my specifications. That is a wonderful thing because I will not only be able to wear Rabbeinu Tanm tefillin according to mt views and I can afford to pay the price he asks. In addition he can obtain good battim and obviously he will use the writing of the Beis Yosef even though I have clarified that other alternatives are also valid as all are from Sinai but that is that is the normal practice.