This is interesting but gun type bombs are not feasible for plutonium. The fission rate is too fast and would destroy the plutonium in a "fizzle" instead of a large explosion. This device could not use plutonium because it would have to be much heavier and longer.
The distance required to accelerate the plutonium to speeds where predetonation would be less likely would mandate a gun barrel too long for any existing or planned bomber. The only way to use plutonium in a workable bomb was implosion—a far more difficult engineering task.
https://en.m.wikipedia.org/wiki/Thin_Man_(nuclear_bomb)
Also, the "shaped charge" plutonium bomb could not be assembled on site. It is too delicate a job for "spies" to do in a hotel room. This would have to be Uranium if assembled on site, and it may not even work then.
I wonder if the magazine knows this. Maybe they were fed incorrect info, since this may have been classified at the time.