It appears to be a factory Schnabel BTFE. And your Field barrels do have the Reinforcing Wedge generally used with the heavy BTFEs

Schnabel above and the Long Flat below





It would be very interesting to know how the single Field LRWF with a BTFE got with your Specialty, or if it was a later addition.
If you are a LCSCA member, Dr. Jim will check the Field SN shipping record for you
https://lcsca.clubexpress.com/content.aspx?page_id=22&club_id=43784&module_id=245742