273 or 318 or both help

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If you want to work with the parts you have, then throw the good 273 crank into the 318 and call it a day. That also addresses the crank flange/convertor issue. Use the rest of the 318 rotating assembly, and all the 273 accessories (timing cover, water pump, pullies, power steering pump & brackets, etc.) Also use the 273 oil pan, pickup and dipstick/tube. Using the 273 manifold on the 318 will allow you to retain the stock Barracuda's throttle and kickdown linkage.
Using all the 273 peripherals on the 318 makes it a virtual bolt-in and it will look perfectly stock.