Lots of money in the old cars for parts. About 35 years ago I worked for a gas station (back when they still had full service and mechanic bays) and he would buy old cars and have us strip parts off on third shift while it was slow. His house (about 10 acres) was filled with barrels of parts stripped with tags identifying what make/model it was stripped from. When he would get a car in the garage for repairs he often sold them a used part quickly paying for the car itself then pure profit from there.

Your dad could probably partner with some small business mechanics, if he provided them with a list of the cars that parts could be stripped from. Especially if he targeted mechanics specializing in older cars. If they have any drag strips near you, often many of the drivers are mechanics and have a higher likelihood of working on older models.