Gavin and TJR-
Belive it or not, as long as the welds are sound, step-notches installed on frames makes the frame stronger. The notches are typically at least the same gauge of metal as the frame, if not thicker, and fully boxed. I've seen a few bagged truck get into accidents and it's the suspension components (panhard bars, link bars, etc) that fail and get torn up, not the frame.
Tony...looks good so far. How low do you get? Have you thought about a raised tranny x-member?