No, a 1987 Chevy truck 10-bolt rear end will likely
not fit directly into a 1989 Chevy truck without modifications. While both are 10-bolt axles, there are subtle differences in mounting points, spring perches, and possibly even the width depending on the specific model and trim level of both trucks (e.g., short bed vs. long bed, different axle ratios).
You'd need to carefully compare the dimensions and mounting points of both rear ends to see if they are compatible. Even if some dimensions seem close, small differences can prevent a direct swap. It's highly probable you'd need to modify either the chassis or the rear end to make it work, and that's not a trivial undertaking.
