No, I cannot get my pinky onto the bottom of the pre-rail 3913TSW or CS9 (which both use the same 7 round magazines.) On a regular 3913, I can just barely squeeze my pinky onto the edge of the flat factory magazines.
And yes, the body of the 39 magazine is approximately 1/4" longer than the body of the 3913 magazine, but it has a flush baseplate. With the addition of the 1/4" baseplate to the 3913 magazine, they are effectively the same length when inserted in a 3913.