Here's some replies I received so far (these were Chrysler engineers who were in the thick of all things racing & high-performance back in the day):

Hot test at M&I.Early Cross ram A990 motor.

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For what it’s worth the Spark plug wire boots look like early 64/65 race Hemi that are total different than 66 up street Again the picture is not that clear on my I phone.

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I’ve guessed about this before, I’ve always thought the early gen two engines where built in Marysville at the MCI plant. This looks like 64, carter carbs and K heads. It’s a hot test stand. Probably no load and I have no idea what kind of instrumentation they had on it. I know at Trenton, when Al Nichols worked on their hot test set up, they had lots of pressure and temp channels to make sure all was good to go. And of course, look for oil and coolant leaks.

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I’ll second Greg’s thoughts. I have seen this picture before, as well and the consciences is this is a hot test at M & I, where some of the Hemis were built.