* Definition of "fit": Does "fit" mean it physically fits in the engine bay, or does it include considerations like clearance for accessories (alternator, power steering pump, etc.), exhaust manifolds, and proper functioning? Just fitting the block doesn't mean the whole drivetrain will work.
* Specific engine dimensions: Even within engine families (like a small-block Chevy vs. a big-block Chevy), dimensions vary based on year, model, and specific modifications (e.g., aftermarket intake manifolds).
* Transmission: The transmission's size and mounting points will also significantly impact what engine can be used.
While a stock 305 cubic inch (5.0L) small-block was original to the '88 Monte Carlo SS, some people successfully install larger small-block Chevys (like 350 cubic inch/5.7L) with minimal modification, mostly involving exhaust and possibly accessory bracketry. However, a big-block Chevy (454 cubic inch and larger) would almost certainly require significant modifications to the engine bay, firewall, and possibly even chassis bracing to fit.
In short: Without any modifications, the largest engine that will reliably and safely fit is likely a slightly modified 350 cubic inch small-block. Anything larger is highly unlikely without substantial modification, and the extent of the modifications will depend on the specific engine.
