This is not well known, however, Winchester used several little known sub contractors including Intertype Corp, receivers. These Intertype receivers were marked with a T on the rear slope. Winchester was directed not to scrub the T off as it was for identification purposes. Here is a picture of mine along with some interesting information collected by the now defunct Carbine Club. Also noteworthy are the double + marked recoil screws in this serial number block so I included a summary on them.
(https://i.postimg.cc/15F6x6S0/w-1.jpg)
(https://i.postimg.cc/xCqJ6Ngz/w-3.jpg)
(https://i.postimg.cc/G3Zjhm6b/w-9.jpg)
(https://i.postimg.cc/qgVgfYbd/intertype1.jpg)
(https://i.postimg.cc/MHGK76YW/intertype2.jpg)
(https://i.postimg.cc/BZ8g0KYh/w-11.jpg)