The North Korean Air Force has about 100 MIG15, 100 J5/MIG17, and 40 J6/MIG19. These planes need to be replaced as soon as possible.
China has a total of 308 J10A and J10S. North Korea can also replace some old MIG21.
North Korea also has about 20 SU7 and 80 Q5.
China has 170 JH7A and 100 JH7s(30 of which have been retired). China can use 100 JH7 as a gift for the business, and North Korea can replace all SU7 and Q5 with them.
In this way, North Korea will have about 220 J10A, 88 J10S, 90 MIG21, 46 MIG23, 30 MIG29, 100 JH7 and 35 Su25. North Korea will have 438 4G fighters.
South Korea has about 60 F15K, 180 F16C/D and 60 FA50. A total of 300 4G fighters.
The gap between the air forces of the two countries will be significantly weak. North Korea is worth spending 19 billion CNY ($3 billion) on that.