Sounds like you already have the $ needed for all 4 years which is a good thing from an investment perspective (don’t need to invest aggressively to meet your goal).
You could front load a 529 with $85k and invest it conservatively just so the earnings are tax free for year 3&4. Where you have it now, the interest is taxable. With the remaining 115k you could do a CD or bond ladder maturing each of the first few years of tuition.