Brooks James said

The plot thickens considerably, the block has a 4.250 bore, thus A 426
Original steel factory head gasket, numbers correct, the valve cover gaskets are hard and will require a sharp scraper to remove they've been on for so long.
I'm thinking that it's a virgin, never opened up, which would mean it's a 426 from the factory

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Brooks James said

Edit, Chrysler museum permanently closed, the one I need 0ut of 3
Archives material is apparently build sheets, brochures, etc
Can't seem to find mechanical/ engine specs material

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