.040 over is a standard repair bore. Difference in displacement is minimal, made only a few ci. Cooling won't be a problem either unless you do some mods that make horsepower. However, a fresh motor may put a strain on an old, clogged radiator and cause overheating where it didn't before the rebuild.
its simple math , pie x r squared x stroke = displacement,a 318 is 3.91 bore with a 3.31 stroke so//// 3.91 040=3.95
pie,3.1416 x r 1.975 =6.204 x r1.975=12.254 xstroke 3.31= 40.561 ci per cyl x 8 cyl=324.49 ci. You will now have
a 324.49 instead of a 318.now forget the 318 and go buy a 360! its the same eng. just more stroke more bore (4.0x3.58)