* The transmission itself: A 1991 Camaro RS could have come with a few different transmissions. The most common were likely a 700R4 automatic or a 5-speed manual (likely a Getrag). The bellhousing pattern is the same for both, but the specifics of the transmission (internal components, gear ratios) will affect how well it works with the 305.
* The 305's condition and modifications: A stock 305 is relatively low-power compared to some other small-blocks. A heavily modified 305 with high horsepower and torque could overwhelm a stock automatic transmission, leading to premature wear or failure. A manual transmission will handle more torque, but a significantly modified engine might still require upgrades to the clutch.
* Intended use: For casual driving, a stock 305 and a stock automatic or manual transmission from a Camaro RS will likely work fine. For performance driving or racing, you'll likely need upgrades to the transmission or possibly even a different transmission entirely to handle the stress.
In short: The engine will physically fit, but compatibility depends on the specific transmission and the power output of the 305. If you're modifying the engine significantly, or planning performance driving, consulting with a transmission specialist is highly recommended.
