Volvo most likely would have used a single stage baked on Enamel on the 140. The lacquer, while not being original, is probably the easiest to apply. It dries almost as fast as it lays down. Duplicolor advises to use a lacquer clearcoat to make the finish a little more durable plus a base/clear is a more forgiving of mistakes and being lacquer, it can and should be buffed out after about 24 hours.

However, an enamel is more durable, but is more difficult to apply. It takes long time to both dry and fully cure and is prone to dust specks and orange peel during application. You have to wait about a month to buff out un-hardened enamel. It may be difficult to apply enamel properly to a large area such as a roof with a rattle-can, so the lacquer may be the best way to go.