Engine-Specific Needs:
* Engine Mounts: The Pontiac 455 and Oldsmobile 403 have completely different engine mounting points. You'll need custom engine mounts fabricated or sourced from a specialist who makes them for this specific swap. This is often the biggest hurdle.
* Exhaust System: The exhaust manifolds or headers from the 455 Pontiac won't fit the 1979 car's frame. A completely new exhaust system will be needed, likely custom-made.
* Wiring Harness: The wiring harness for the 455 Pontiac will be different. You'll either need to modify the existing harness extensively or source a harness specifically for a 455 Pontiac in a similar-year chassis, and then adapt it to your 1979 car.
* Cooling System: You might need to adapt the radiator and cooling hoses, as the 455's cooling requirements may differ.
* Power Steering: The power steering pump and lines may not be compatible. You'll likely need to adapt or replace components.
* Alternator: Similarly, the alternator and its brackets might need modification or replacement.
Transmission-Specific Needs:
* Transmission Crossmember: The 4-speed manual transmission's crossmember will be completely different from the automatic's. You'll need a crossmember designed for a 4-speed in your 1979 car's chassis. This often requires fabrication or sourcing a used one from a similar-year car with a manual.
* Driveshaft: The driveshaft length will be wrong. You'll need a custom-length driveshaft made to fit the 4-speed transmission and the rear differential.
* Clutch Linkage/Hydraulics: You'll need a clutch pedal assembly, linkage, master cylinder, and slave cylinder to operate the manual transmission. The 1979 car was originally automatic, so these components are entirely missing.
* Bellhousing: The bellhousing from the 455/4-speed combo might not bolt directly to the 455 Pontiac if it came from a different year or model. You need to ensure proper compatibility.
Other Considerations:
* Fuel System: You'll need to check fuel pump compatibility and possibly upgrade the lines and filter.
* Computer/ECU: While the 1975 455 might be carbureted, you'll need to ensure the ignition system and carb are compatible with the rest of the vehicle's setup.
* Mechanical Expertise: This swap requires significant mechanical skills and tools. Unless you have extensive experience with engine swaps, it's recommended you enlist the help of a professional mechanic specializing in classic car restorations.
In short: It's doable, but very challenging. The cost and time involved will be substantial. You'll be spending a lot of money on parts and potentially even more on labor if you don't perform the work yourself. Carefully weigh the cost and effort against the value of the final result. Before starting, it's advisable to consult with experienced mechanics or online forums dedicated to Pontiac and Trans Am restorations. They can offer valuable advice and insights based on similar projects.
