I just had my local body shop replace the cab corners, inner and outer rockers, front and rear lower door pillars, outer floor, upper floor and front and rear cab mounts on both sides of the cab on my '66. He told me that they had to use jacks and porta powers to keep the cab in shape. So yes I'd say it would be a very good idea to brace your cab and just do one side at a time. You'd be surprised how much the different parts of the cab rely on one another for support.
