You should be able to find post to explain the differences on a real hemi booster. Stud pattern and size. Unique and hard to find bendix MC for E body, and the hemi offset brackets. Believe DR Diff uses the non hemi booster bolt pattern and booster arm, but he can confirm
that.

If your a disc brake E body with orig KH set up you can certainly go with the 70 B body master cylinder. Slightly different shape but 1 1/8" bore and the 70B used the same disc brake hardware as the E body (70-72 B/E).

Now if your manual drum you do not need the offset bracket, and that makes it a lot easier on engine maintenance.