The gas tank and parts of the undercarriage (mainly floor pans and tunnel area) on my car has definitely been undercoated and it appears factory. Exhaust has been changed. VN 5A car.
Pulled my documentation out this week looking for a reason the inner door sticker had been removed on my driver's door. I have an original order form for a LH door panel, so it was replaced under warranty for some reason. Meanwhile I came across a receipt from the original dealership dated Nov 4, 1969, stating under seal the car for a cost of $11.00. I just recently had the under coating removed via dry ice blasting. It revealed the rear inner fenders was painted the body color (I assume this was later undercoated at the factory) and there is also body color over spray on the floor pans under the car. The tunnel area was painted black over a brown looking primer. This explains why my car had so much undercoating.