Jason, I also wondered about motion blur but supposed that even if there was some finger or shutter impulse, the OP's rig probably settled down in a small fraction of 2 sec. But you are absolutely right, if there was any continuous subject motion then it might well show up.
I am not familiar with this particular taking lens, is it really optimal at close focus? Does one use a diopter to get that kind of magnification? Is the focus match precise enough with a tlr to do this kind of thing?
(N.b. I still say that the scan looks good as far as I can tell!)