That pic dates to an UNREP sometime during 1956, along with a few more, very rare (for the time) color pics, from the same event. I also have pics dating back to 1955 and forward to 1957 showing the identical fit, in all respects. The white covers for the 40mm muzzles and (I'm presuming) also white covers for the recoil springs are unique, in my experience.
There is other evidence suggesting that exposure/corrosion of these guns was a problem, as the quad-40s facing into the wind/seaspray were progressively removed, while the others left in place. The pair on the forward bow (only) were removed by 1955, and the quad-40 on the forward bridge - again, only this one - was removed in 1957.
I can post the whole set of Boxer reference pics located so far, if you guys are interested.
Meantime, just wait 'till you see my own depictions of those 40mms in there - along with a ton of other resin details, to match!