You also have to avoid the flywheels for the small block 400 engine. Those engines were externally balanced, unlike the sixes and the pre 87 small blocks. As I think about I believe they were all the larger 168 tooth wheels so you shouldn't have to worry about it if you are sticking with the 153 tooth versions.
The bellhousings are different. The smaller flywheel uses the one that has a straight side where the starter nose installs. The larger flywheel bellhousing has a very noticeable round bulge for the starter nose.
