Generally, you would start with the casting number off the rear of the block. This is a 6, 7 or 8 digit number that is raised from the surface of the block, cast right into the block material. It is on the driver side, just forward of the back face of the block where the bellhousing bolts on. It's usually gunked up with grease and debris, so that it will take some cleaning with solvent and a toothbrush to be able to read it. Once you have that number, you would fine tune it with the suffix number off the front of the block that you have provided. Once you know what the block is, remove the valve covers from the heads and find the head casting number in between the valves.

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Chevy Small Block V8 Casting Numbers - Mortec
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