Will the intake manifold off 1986 350 fit on 1988 35 0 with throttle body injection?

No, a 1986 350 intake manifold (likely carbureted) will *not* fit a 1988 350 with throttle body injection (TBI). The port locations, bolt patterns, and overall design are significantly different to accommodate the TBI system. The TBI system requires a specific intake manifold designed to integrate with its throttle body and fuel injectors.