I cannot make out the SN from your picture, so it is not possible to confirm if the frame SN is consistent with R-R manufacture. The full list is here: Model 1911A1 Dates of Production

When these went through arsenal rebuild and refinish, there was usually some arsenal mark stamped on them. Arsenals did not have any reason to keep original parts together, so it is not unusual to find mismatched slides and frames. R-R manufactured more M1911A1s than any other manufacturer, so they are the most commonly found. Aside from the 500 made by Singer, the most uncommon is Union Switch and Signal. I had one of those at one time. P.S. - the GI ammo box is from after WWII (1954-69). More contemporary with Vietnam use. Most WWII .45 ACP ammo had steel cases.