mystery big block

I have a '75 duster with a non original big block in it which I was told by the shop I bought it from was a 400 (they did not install it, they accquired it with the engine in it). However, the guy at the local muffler
man who put my exhaust on says he's almost sure its a 440. I looked for the engine ID number in both the locations listed in my Hanes repair manual for these two engines, but did not find the numbers, I'm assuming due to the crappy repaint the engine seems to have undergone at some point. The block casting number is 4006530-400-3. I checked this out on google and found that the casting number 4006530 was used on '74-'78 440s and '76 to '78 400s, but no info on the last 4 digits. Does anyone know any other way I can tell what this engine is? Some way to measure the deck height maybe? Is the "400" in the casting number indicative of displacement? It would really be helpful to know which engine this is so I can order the correct parts for the upcoming build I'm planning. Any advice would be appreciated. Thanks!
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It has been at least 25 years since I worked on those engines. It seems to me that I would look at where the distributor was located or the way the spark plugs went into the cyl head, I just cant remember. Do a google on it and Im you all your questions can be answered.
Glenn Beasley Chrysler Tech
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Hard to say, depending on what distributor is in the engine. Assuming aftermarket ? Most are made for 440 & are used with a spacer for the 400
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I didnt mean what distributor it had but at which point it is installed in the engine
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Managed to figure out that it is a 400 due to the lack of the machined plate adjacent to the distributor which would indicate the displacement on the RB engines, including the 440. Also managed to figure out that it is a '76 engine because the trans that came with it utilizes a 3 piece throttle rod assembly which, according to my Hanes manual, was only used in big block applications in '71-'73 and '76. Since the engine is a '76-'78 casting, I can rule out '71-'73. Thanks for your help!
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