1. Engine Block Casting Number: Look for the engine block casting number, which is usually located on the front or side of the engine block. For a 2-bolt main 454, the casting number will typically end with "010" or "991". For a 4-bolt main 454, the casting number will typically end with "482".
2. Oil Filter Location: The oil filter on a 2-bolt main 454 is typically located on the driver's side of the engine block, while the oil filter on a 4-bolt main 454 is usually located on the passenger side.
3. Engine Mount Brackets: The engine mount brackets on a 2-bolt main 454 are located at the front and rear of the engine block, while the engine mount brackets on a 4-bolt main 454 are located on the sides of the engine block.
4. Cylinder Heads: The cylinder heads on a 2-bolt main 454 are typically flat, while the cylinder heads on a 4-bolt main 454 are typically raised.
5. Spark Plug Wires: The spark plug wires on a 2-bolt main 454 are typically routed over the top of the valve covers, while the spark plug wires on a 4-bolt main 454 are typically routed through the sides of the valve covers.
Note: These are just general indicators, and it's always best to consult with a professional mechanic or refer to the engine manufacturer's specifications to confirm whether your 454 marine motors are 2-bolt or 4-bolt main.
