2/4 Bottom set against nit almost 400 BB deep

[pp262]

Call, call a blank turn, probably fold river if he shoves.

[UR75]

he may fold to any kind of 4-bet without the nutFD or an overset and as deep as you are he might even fold FD if you really think he has been playing nitty postflop as well. Seems like a call then try to get it in on blank turn since I can't see him checking turn after 4-betting. if you think he will c/f to any large bet with FD on non-spade turn then you might want to just push on his 200 bet making it possibly look like you have overs and FD to snag him with his big overpair.