Hard to say for sure, Andy. Yours is only 6741 digits above a known USMC Garand (1464413), which itself is only 42 digits above Guam Garand 1464371 so it's relatively close. It would be super if the Springfield Research Service website was still posting their serial # lists, or even if the books were still available for purchase. The serial # patterns seem to offer clues to the disposition of rifles that are close to but not listed by SRS.
The earliest "Guam" Garand listed that is part of a serial number "run" was SA 1142472, made in January 1943, not long after the USMC fighting troops started to realize the worth of the semiautomatic Garand over the bolt action M1903. I'd be curious to learn the percentage of Grands issued that weren't in the "Guam" ranges that have annealed heels. It begs the question of whether the USMC specified that any Garand they accepted had to have an annealed heel? The two 6 digit Garands listed weren't, nor was the last, made in Nov. '43 and only 1 of the remaining 27 wasn't annealed.
Duff may have been speculating when he wrote his piece about the Guam Garands back in 1996 but as we've seen in recent issues of the GCAicon Journal, there have been M1icon Garand relcs found in and around Bastogne that also fall in close serial number ranges too so it seems to support his argument for the Guams' relationship to the 3rd Marine Division.
BTW, none of the "Guam" Garands are Winchesters, and I once owned SA # 1472046, it also had an annealed heel.
HTH