Scott, What you could do is first paint the "hard to get at" parts of the panels and the car like the mounting flanges on the fenders, inside the hood, inside the fenders, inside the fender wells on the body, bottom of the running boards (if any), inside the trunk lid and edges where trunk weather striping goes, firewall, around the window openings (no glass in car), door edges, etc. and then assemble the parts on the car so they all fit really nice. Then loosen the fenders (with no welting) and paint the entire car one final time. By doing this, you don't have to worry about not getting any paint into "hard to get at" areas. If you paint panels at different times and then the body another time you might end up with what appears to be "off colors" or different shades of the same color.
I painted my 40 with Martin Senour 8800 black acrylic enamel with hardner which is an off the shelf paint color. I didn't have to worry about the paint being mixed differently each time. But. if I was using a "formula paint" I would have painted the car one time all at once so as to make sure the color didn't vary.