It could well be that the Guamanian police authorities were left with more than 30 Garands after they and U.S. forces completed the post battle mop-up of Japaneseholdouts on Guam and some time in subsequent years. How did the parts composition of your 2.435xxx compare with the Duff's data sheet of 2.466215 listed in his "The M1
Garand: World War II"?
Where Guam is a US territory therefore not subject to importation laws it probably wouldn't have been real difficult for an M1 to find it's way back to the States in the period from the end of WWII to the 1990's when the Guamanian authorities decided to divest themselves of their remaining inventory of Garands.
One interesting thing I noticed in comparing data sheets of the certain "Guam" Garands with my 1.5618xx is how frequently the receiver heat lot #'s changed. For example, the gap between the two closest numbers Duff lists in his monographs is 81 digits. Mine falls in between those two and all three have different receiver heat lot #'s.