69 Dart 340 Swinger

I finished blocking the hi build primer, and shot another coat of primer. Once the car is back together (I still need to do one door and the trunk lid) I'll reassemble the car and block it one more time.

Question. I plan to paint the undercarriage semi-gloss black. Should I paint the body (gold) first then the undercarriage, or the other way around. I'd hate to get overspray on either part, but looking for advice.

Thanks,
George