There have been several postings from people [on the WWW Message Board] just beginning a restoration for the first time. Everyone is anxious to dig in and get'em apart (it's normal!). Some patience and planning at this point in the project can save an incredible amount time and frustration at the other end of the project.
If the car hasn't been disassembled yet, it's a golden opportunity to determine what fits and what doesn't, doors, hood, fenders, bumpers, etc. Remember, if it doesn't fit NOW, it won't fit LATER. Look more closely at everything! What doesn't seem to offensive on an unrestored car may bother you much more when the car is pretty and shiny!
It's also a good time to do any heavy body work. It's MUCH easier to major or minor body work on a fender, etc., mounted in place than sitting on a bench. Major work will also affect fit. If all dents, patches, etc., are taken care of prior to stripping or blasting, you then will have an ideal surface for fillers or primer.
If you choose to replace fenders, fender brackets, etc., with new reproduction parts THEY WON'T FIT without modification. Attempting to install a shiny black fender bracket won't be fun when you find it needs to be heated with a torch to reshape, then repainted.
If you are not so fortunate as having the car in one piece, consider assembling as much as possible using the parts you intend to use i.e., new body mounting blocks and rubber pads. You will likely find a few surprises that are much easier to deal with at this stage. It will also help determine what parts are missing. Almost all frames have at least a sag in the right frame rail at the rear motor mount from the torque of the engine over the years. If the car is already apart deal with it now before fitting.
A little patience, planning, and effort at the front end of the project will more than pay for itself at the back end in saving time, frustration, and likely better quality.