I wouldn`t worry too much about the gaps at this point. I`d say you could get that done pretty well, but you have to know if if the frame is straight first. Looks like it took a serious hit... If the measurements are within tolerances ,I would cut off the inner fenders and coil support, get all new bodyparts lined up before welding anything, and go from there. If measurements are not within tolerances, ask the bodyshop that will pull the frame if they want it with all the parts on or not, before you start cutting.
I have a shop manual with all measurements if needed.