Blast media

Remember when the factory built these cars that bare metal went into a primer dipping vat and that got into ALL the cracks an crevices.
I think back a few decades ago when I took hoods to K.C.. Mo for chemical dipping. Yes they came out 100% clean, but that hood with the frame and top skin, unless dipped, no way to blow epoxy primer into all those inner spots.
Having a rotisserie helps a bunch, but I have never got all the sand out of a car I had sandblasted.