Dollar cost average in over the next six months or so into a low-fee index fund, and then start to make staged withdrawals as your target approaches.

The 529 plans give you some tax advantages, but then you wouldn't have the funds available for a mission.

Using it in a brokerage account doesn't give you much of a tax advantage, but does give you twelve years of market compounding, which will be offset a little when you realize those capital gains upon selling the position.