Look at my avatar. The casting on the side of the block tells you what it is.
Here is a 440 RB casting.
For era-correct block, look for this number (ignore the # after dash)!!
440 "RB" Engine
1966-78 • 4.32" bore x 3.75" stroke
If there's one golden rule of '60s engine design, it's simply bigger is better. Thus, the 440 cubic inch RB engine was born. Although debuting at a stout 365 horsepower in top form, the 440 was overshadowed by the Street Hemi which was released in the same year. But it didn't take long for the 440 to make a name for itself. In 1969-70, the 440 reached its highest state of tune with the fabled 6-bbl version rated at 390 hp. This number declined slightly in 1971 to 385 hp, which was the last year for the 3x2-bbl option. The 440 remained in production until 1978, although by then it had been strangled by the same unleaded fuel and emissions monster that ultimately killed all of Detroit's big blocks. But the fact remains that, at least on the street, the hot-rod 440 six bbl. engines of the '69-70 period would often humble a similar Hemi-equipped model.
and more...
RB BIG BLOCKS
CASTING # C.I.D. YEAR GROUP
1852029 413 1962 RB (Max Wedge)
2120529 413 1959-65 RB
2205697 413 1959-65 RB (Pass.car)
2468030 413 RB
2406730 426 1963-65 RB (Wedge)
2468330 426 1964-71 RB (Hemi)
2658836 426 RB (Industrial)
2536430 440 1966-72 RB
3698830-440 440 1973-78 RB