well, if i remember correctly, the 274 could be had with a 4 barrel, where the 318 could not
that tells me all i need to know
but i will admit, i enjoy the back and forth on this
...but the 273 was discontinued in 1968 while the 318 got a 4 barrel in the early 1980's and lived on into a second generation (1992) until 1999, ending up MPI and 230 NET HP.