If the car was on a rotisserie you could put some over reduced epoxy primer in a squirt or spray bottle and use it to get primer into places where the sun doesn't shine. The bottoms of these cars were full of runs and drips from the oem dip process so recreating those runs would be more authentic than just spraying it with a gun.

Some places you won't be able to reach, but as long as you have primer around the places where the water might get in that would be better than nothing.

The hoods on these cars only have primer overspray dust underneath the bracing. If you turn the hood upside down you can pour watered down primer on the bottom and have a helper help you tilt the hood around to get primer back up where no paint gun can reach. Once it's dried you can feather out any runs and keep going.