* Bellhousing: The TH400 uses a different bellhousing pattern than the transmission likely originally in the Caprice (likely a TH350 or possibly a Turbo Hydra-Matic 200-4R, depending on the options). You'll need a TH400 bellhousing that's compatible with the 350 small-block Chevrolet engine.
* Torque Converter: You'll need a TH400 torque converter that's the correct stall speed for your engine and intended use.
* Driveshaft: The TH400 is longer than a TH350, so you'll likely need a new driveshaft or to have your existing one shortened.
* Crossmember: The transmission crossmember may need modification or replacement to properly support the TH400.
* Wiring/Controls: The shift linkage and electrical connections will need to be adapted. You might need a new shifter.
In short, while the TH400 is a common and robust transmission, fitting it to your 1979 Caprice is a mechanical project that requires some expertise and fabrication. It's not simply a matter of unbolting the old transmission and bolting on the new one. If you're not comfortable with automotive repair and modifications, it's best to have a professional mechanic perform the installation.
