Fold IMO. 88 and 87 make sort of sense, but only 88 strikes me as worthy of a river shove from a passive player, and there are only 3 combos of 88 out there. Given stats there are plenty of JT, QT, T9, hands out there that a very consistent with a river shove and there are like 32 of those three alone. Club draws with a Q, and from some fish even a 6 or 9 get there, has he peeled one off with 54 on the flop? Combos of hands that beat us that make sense from a 45/6 are probably way more than 3 times those that make sense that we beat.

Adding some subjectivity: when passive fish shove the river, they have it more often than not. (NLHE-T+P). This would lead me to put more probability on the high-end of his range for me.