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I don't assume anything so I'd pull both valve covers and write down the casting numbers and post them here. They're located pretty much in the center of the head and hopefully they are a matched...

If that is IM it's a 69 350 255hp with a powerglide tranny used in passenger cars and police applications.

Small Block Chevy Engine Codes - Page 4

First off you need to verify what you have, get the numbers from the pad at the rear of the drivers side of the block and post them here.
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