* Engine Mounts: You'll need custom engine mounts to fit the 350's dimensions to the Fleetline's chassis. These are rarely available off-the-shelf and will likely require fabrication.
* Transmission: The 350 will require a different transmission than the original. You'll need to source a compatible transmission (likely a TH350, 700R4, or similar) and adapt it to the engine and the existing drivetrain. This involves new bellhousing, driveshaft modifications (length and possibly yoke), and potentially a rear-end gear ratio change to match the new engine's power band.
* Exhaust System: The exhaust manifolds and system from the straight-6 are completely incompatible. You'll need a custom exhaust system fabricated to fit the 350.
* Wiring Harness: The 350's electrical system is different. You'll need to either adapt the existing wiring harness, or more likely, install a new harness designed for the 350.
* Cooling System: The 350 generates more heat than the straight-6. You may need a larger radiator, electric fan, and possibly an upgraded water pump to ensure adequate cooling.
* Steering: The added weight of the 350 might affect steering, potentially requiring adjustments or upgrades.
* Firewall: The 350 might not fit through the existing firewall opening without modifications. This might require cutting and welding to enlarge the opening.
* Body Modifications: You may need to modify parts of the body to accommodate the larger engine, such as the inner fenders.
* Fuel System: You'll likely need a new fuel tank, fuel lines, and possibly a fuel pump to support the 350.
In short: While possible, this is a major project best undertaken by someone with significant experience in automotive fabrication, welding, and engine swaps. It's not a weekend project. You'll likely spend considerable time and money on parts, fabrication, and professional assistance. There are many resources and online communities dedicated to classic car modifications that can provide guidance, but thorough planning and preparation are essential.
