I am planning on swaping an 89 tpi (LB9) motor into my 91 RS (LO3) and I am not sure if the connector on the fire wall (drivers side)pin assignment is the same or if the cars interior wiring has to be reworked.

 

Change the harness that goes from the engine to the ECM (as well as the ECM). Everything from the ECM to the rest of the car should be okay (unless VATS - I don't know enough about that system to say).

Guy here swapped TPI into his '90 TBI RS, rewired the TBI harness to work with the TPI ECM. So, it can be done, but don't ask him how many hours he spent doing it.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. Cat-back from '91 GTA, ZZ3 intake, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 w/'87 LB9 block, ZZ3 cam, ported World 305 heads, Hooker headers & y-pipe, 3" Catco cat & 3" cat-back).
57 Bel Air, my 1st car. '66 396, 9.7 CR forged TRWs, Weiand Action+, Edelbrock 1901 Q-Jet, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 600 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).