One method of getting plates to line up is to make up T pieces from scrap stringer material and a series of wedges from a scrap piece of 1/2" plate. Make the taper at different gradients. Weld the T on one side only onto the already fixed plate and gently tap the wedge in until the plates are lined up perfectly. When the plates are welded together then a hit or two on the opposite of the T from the weld will break it off. With a quick trim it's ready to use again.

Fine line up work on a Radius Chine R434. Here we have small tags tacked on lining every plate up perfectly. After the entire hull is plated the full welding up of the entire hull will take place.

G clamps are quite effective on most plates. Don't try and save money here. Buy good quality. Six to ten clamps will be sufficient for 95% of jobs on any of our steel boats. They will come in handy right up to launching day.