I did the front frame rails first with it on the ground and no bracing. We hung doors, fenders and hood back on it and everything lined up great, no worries. I then put it on the rotisserie, put the 1x3 frame rails in, cut out the floors & replaced one side at the time. Did all of that without any bracing and I paid a big price. The body shop was pretty far into it before they hung the fenders and hood again only to discover that the front of the drivers frame rail was 1 1/2" higher than the passenger side. It had to be put on a frame table and pulled back into shape but the good news is I now know it's square and straight. That was a costly lesson, so yes make sure you brace yours well. I would cross brace the interior from the front edge of the inner rocker to the opposite strut tower but hopefully someone that has actually done it will chime in.