1977 cougar info help...I know its not a dodge

The 400 is a tall 351M, It's not a Big Block but it does have a big block bolt pattern and a C-6 tranny. Not rare at all. Neither is the fact that it has a 9" rear. Almost all Ford sedans of the era had 'em. Check for rear disk brakes, that would be desireable but only in a parts value sense.