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!