There are two types of 3646 Case Main Bodies to consider when building a 3646 Project.
Types A,B and C: The early Cases Type A, B, and C were non- symmetrical although I am informed that a few Type C were symmetrical. This means that the shape on the top of the Case is not the same as the bottom. The bottom of these cases are usually a little more flatter than the top. This case available on the Vintage Watch Parts website, its known as the Standard Bezel Case or Type C.
Type D,E,F,G: These Cases were symmetrical, the top of the case is the same as the bottom although there is still a top and bottom to the case as the machined surface for the Bezel and the Case Back varies slightly. This case is also available on the Vintage Watch Parts website, its know as the Tall Bezel Case or Type D.
Lug Holes: Lug Holes are "without internal bores" this means the lug holes are not drilled through the case but about half way through. I believe this was to ensure the Cases stayed water tight. The Lug Bars are 1.8mm thick, and are now formed on a small jig to ensure the radius of each curve are the same.
The images below show the various Case Shapes, both symmetrical and non symmetrical.