I understand how to field-strip my Sig Pro, but how do I reassemble it?

The manual included with Sig Pros sold in the US incorrect states that reassembly is simply done in reverse, which is not accurate. The European manual is clearer about this issue.

The correct way in which to reassemble the Sig Pro is to first install the slide so that the rear is flush with the rear of the frame, as though the pistol were assembled, with the slide in its forward (closed) position. Next, insert the slide stop lever through the frame, which guarantees that it'll also go through the elongated hole in the barrel lug. The final step involves retracting the slide until the disassembly notch matches up with the slide stop lever hole, then pushing in the slide stop lever until it clicks. I find that holding the pistol flat, with the left side facing up, helps, and prevents the slide stop lever from rotating during the final step.