The possibility an An-2 could perform as a nuclear weapons delivery system has about about the same chance as a Cessna 172 does.
The slight problem with your claim the An-2 can deliver a bomb is that the assumed weight of just the weapon, 10,000 lbs, exceeds the published loaded weight of the An-2. Since it's doubtful the North Koreans have succeeded in miniaturizing their bomb to the extent the Western nations have, it is widely assumed the device is the approximate size and weight of WWII era bombs, with a similar yield of 12-15 kilotons.
Then there's the problem of fuel, crew, etc. I know, since you're Henning, it's just details you can easily overcome. A TPE-331 could be installed in place of the 9 cylinder radial. But that actually won't help at all.*
Crew: 1–2
Capacity: 12 passengers
Length: 12.4 m (40 ft 8 in)
Wingspan: ** Upper wing: 18.2 m (59 ft 8 in)
Lower wing: 14.2 m (46 ft 9 in))
Height: 4.1 m (13 ft)
Wing area: 71.52 m² (769.8 ft²)
Empty weight: 3,300 kg (7,300 lb)
Loaded weight: 5,440 kg (12,000 lb)
Useful load: 2,140 kg (4,700 lb)
Powerplant: 1 × Shvetsov ASh-62IR 9-cylinder supercharged radial engine, 750 kW (1,000 hp)
Since it's about 4,500 miles from Pyongyang the Seattle, that presents another small problem.
*Russia has pursued its own An-2 turboprop modification. The Chaplygin Aeronautical Research Institute in Novosibirsk (SibNIA) fitted a Honeywell TPE331 turboprop and a Hartzell five-bladed propeller to an An-2 and successfully flew it "for around 40 hours", the institute's director, Vladimir Barsuk, said in August 2012.
SibNIA claimed a significant improvement in take-off and landing performance and overall handling, as well as a reduction in empty weight.
http://www.flightglobal.com/news/articles/antonov-flies-turboprop-powered-an-2-100-389083/