How do Identify what Small block Chevrolet engine I have with number FO6I6U located on passenger side of facing radiator?

That casting number, FO6I6U, doesn't directly identify a specific Small Block Chevrolet engine. Casting numbers on engine blocks refer to the block itself, not the complete engine assembly (which includes the heads, intake manifold, etc., all of which can change over time). It indicates a specific block casting, but doesn't tell you the displacement (e.g., 283, 307, 327, 350), the year, or even the specific modifications.

To identify your engine, you'll need to look for more information:

* The engine pad: This is usually on the driver's side of the block, near the front. It should have a casting number (different from the one you provided) and potentially a partial VIN or other codes that will help pinpoint the year and some engine specs.

* The heads: The casting numbers on the cylinder heads will tell you the type of heads. This information is important as different heads can significantly affect performance characteristics.

* The intake manifold: The intake manifold can sometimes have identifying markings.

* The carburetor: The carburetor type can be a clue, although not definitive.

* Other markings on the engine: Look for any other stamped numbers or codes on the engine block or components.

How to use the information you find:

Once you've gathered all the casting numbers and codes, you can use online resources to cross-reference them. Several websites and forums dedicated to Chevrolet engines can help you decode the numbers and determine the exact specifications of your engine. You can search for "Chevrolet engine identification" or similar terms to find these resources.

In short: The number you provided is only a piece of the puzzle. You need more information from the engine itself to complete the identification.