I am fairly sure the "boxy" ones, as you call them, came out in 1961. A far better control, if you don’t insist on correctness on earlier motors. The "Snap-in" cables came out in 1979.
While we are on the subject does anyone have or know of where I can get the shorter lever for one of these? mine has been repaired at some point in its life. Also a source for the shifter cable motor end would be great if someone has a source.
Mine is black with a red riveted on plate with Evinrude Simplex on it. It is also a ribbed version. About what year is this one from?