Questions about 1941 distributors.

[vtwinsideways]

Working on a '41-2 Merc flathead to put in my wife's '41 Model 19C. Doing complete resto, so we want things as correct as possible (within reason). It came with a later model crab style dizzy. My questions are, what exactally am I looking for? Were the Fords and Mercs the same and what are the differences between years? I seem to remember reading that there were some minor, although very desirable, improvements during that time frame. I haven't been able to find the article I read that in though. Thanks. Luke