Hmm I'd take the $39m, it's a lot of bloody money, more than enough to live on for the rest of your life. Hell stick it in a *bank* account, not an investment account, and you can live on the *interest* alone from that much cash (2.5% interest, about 975,000$ a year).
Of course I'd make bloody sure that the contract with the local government was airtight and they couldn't just turn around and sell the park in a few years when some bright bulb gets elected.
I don't know about America but there was a case in my own town about a woman who left some prime real estate to the town almost fifty years ago, on the condition it was used as a place for mothers to rest and look after their kids. About ten years ago the council tried to sell it, since the land and building were worth millions at that point, being right in the middle of town, and they almost got away with it until a local lawyer stepped in and had a court look at the original will.
I'd also stipulate that the local government wave as much of the costs involved in the sale (legal fees, etc) as possible.
I do hope he takes the lower price, because those people shouldn't be forced out of their homes. Housing prices are just out of control in a lot of places.