The IISS has a paper addressing the conventional military balance between North Korea and South Korea.

Conclusion

The combination of North Korea’s long economic decline and enhanced US and South Korean military capabilities has diminshed the threat of a North Korean invasion of South Korea. Nonetheless, North Korea retains the ability to inflict heavy casualties and collateral damage, largely through the use of massed artillery. In effect, Pyongyang has more of a threat to devastate Seoul than to seize and hold it. North Korea’s conventional threat is also sufficient to make an allied pre-emptive invasion to overthrow the North Korean regime a highly unattractive option. In theory, US forces could carry out pre-emptive attacks to destroy known North Korean nuclear facilities and missile emplacements, but such attacks could provoke North Korean retaliation and trigger a general conflict.

North Korea cannot invade the South without inviting a fatal counter-attack from the US and South Korea, while Washington and Seoul cannot overthrow the North Korean regime by force or destroy its strategic military assets without risking devastating losses in the process. In this respect, the balance of forces that emerged from the Korean War, and which helped in maintaining the armistice for 50 years, remains in place. None of the principal parties want to fight a war although they are prepared to fight if necessary. In this respect, the balance of forces creates certain vulnerabilities since it places a high premium on carrying out a pre-emptive strike if one side or the other believes that an attack is imminent. The danger is that war will begin out of miscalculation, misperception and escalation, rather than design. As a consequence, reduction of political tensions and conventional confidence-building measures can help to reduce the risk of war.

There's another paper in the Asia-Pacific Journal that pretty much says the same, with more details about how the South Koreans have progressively better equipment (tanks, artillery, aircraft, etc.) than the North Koreans than they did, say, 10 or 20 years ago, with vast increases in defense spending since then.