That is a fairly early block. It requires a grooved cam as there isn't a groove under the rear cam journal found on 1967 and up big blocks. The good news is if that was cast within the first four months of the production run (the 396 came out mid year with the 409 retained through the first half of the year) The block will have very, very thick cylinder walls because it was cast to be either a 409 or a 396 which differ greatly in bore size. If rebuilding it you can have the cylinder wall thickness checked to confirm allowing you to convert your 396 into a 427 or a 481 if you used a 454's four inch stroke crank. with the 409's bore size.