Errata
The Soviets did not want to give Cuba nuclear armed missiles. The Soviets wanted to base missiles in Cuba much the way the US had missiles based across Europe and Turkey.
The FAS article cited below indicates the Soviets sold NK a reactor in 1965 and then didn't have much to do with them. The North Koreans upgraded the reactor on their own, and apparently have done most of the rest of the work themselves.
Without Soviet or Russian help.
I don't think either Russia or China trusts them.
Arf