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Hunter Speed & Kustoms

Hey Rob, sorry for the delayed response. Yup, ID'ing these vintage engines can be tricky. Cool to hear that your dad has one of these 303's and even cooler that you're researching the history. To ID this engine you need to pay attention to the block number, first and foremost. Also helpful to ID the heads. You are correct that the block number posted above is from the rear top of the motor close to the firewall. I posted an additional pic above from the shop manual that lists the numbers for both the block and heads for the 303. If the block number matches, but the heads don't, you still have a 303. By way of example I am using my 303 block but heads from my 371 as they were in better shape and are interchangeable.

Check out these links, you'll find great information.




Hello, just wanting to know if the picture of the casting on the engine, on your 303 rocket motor. Is it located at rear of motor on top close to the firewall, if it was installed.
The reason for my question, is on my dads 1949 oldsmobile 303 rocket motor i want to see if in fact it is by numbers the real deal.As it has the one side fits both exhaust manifolds,which has stamping of gm 555l97, and 555677 on the steel bellhousing cover .As well where might you have found refrence to codes, as you said with yours that you said first year production was yours by way of the numbers.I am young , but am very interested in the history of the old car.Any help would be very appreciated

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