On an 86, it is going to be totally custom with a new tranny to go with the new engine. Then you will have to fab up cross members, motor mounts and then fix the driveshafts to fit the new combo. Plus, the wiring, the plumbing, and the ECU to drive the new motor. No small task.

In short, you would be better off buying a v6 Trooper. Even if it had a blown 2.8, you could still swap the 3.4 and be happy, but putting it in your, while not impossible, would be a long row to hoe.

Good Luck,
Michael