what is the width (diameter) of an A body brake booster?

hello guys i'm new to the forum, but not new to A body mopars. My current A body (66 dart style, canadian valiant) has manual drum brakes and I think I found a brake booster for it but the person doenst know what its off of (obviously mopar though) so i'm wondering what the width across one is from side to side, also the length but thats not as important