No, it won't bolt right in. Because the '84-'86 came with either the 2.8 V6 or 4 cyl the radiator core support is further back than it is on the '87 and up that came with the 4.0L 6 cyl, so that would have to be changed, plus motor mounts, trans mounts, and engine and trans controls. It would be a complete conversion job to get it in.
No, it won't bolt right in. Because the '84-'86 came with either the 2.8 V6 or 4 cyl the radiator core support is further back than it is on the '87 and up that came with the 4.0L 6 cyl, so that would have to be changed, plus motor mounts, trans mounts, and engine and trans controls. It would be a complete conversion job to get it in.
Not to mention the firewall shape won't allow for fitment unless it's radically modified. People I've talked to who have actually done all this work insist it would have been a better idea to just get a later model to at least start with.