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Here's a random wild suggestion. There are a lot of old Sherman tank chassis' in use as the platform under heavy duty logging spar yarders and hydraulic rock drills in the Northwest US and Pacific coast of Canada. The two brand names that come to mind are Madill and Finning. The majority of these vehicles are aging out of service and get parked in logging company yards, or have been parked because of different logging techniques, or simple economic circumstances.

Get your Goofle fingers working to see if you can't find a dealer or auction site that might have your engine. Alternatively, register on dub dub dub heavyequipmentforums dot com. From my limited exposure to that business, you will get immediate and informative answers.