In a lot of cases--they interchange without issues.
early Chevelles----will bolt up (with the exception of the 307 Frame mounts), but the big block will sit higher than it is supposed to on SBC mounts.
I believe the 73-87 Chev/GMC trucks require a different frame mount as well, but the clamshell is the same.
58-64 Chev full size----a BBC will bolt up on the factory v-8 mounts, but not the 6cyl mounts.
Might help if we knew what you were working on.