How many miles would a well taken care of Aurora go before major repairs are required like engine and transmission rebuild or timing chain changes?

First, a timing chain replacement is not a major repair. With today's extented engine life timing belt and chain replacement has become part of routine maintenance. More information is needed to answer this question. Listed are just a few of the varibles involved. What, for instance is the contributors idea of "well taken care off". What type of oil and filter is used and how often is it changed? Where are the miles being put on the car(city.highway, a combination of the two)? Is the car subject to many short trips. What environment is the car driven? How is the car driven. Example, is it allowed to come up to temperature before working hard? Is the automobile operated by more than one driver. What kind of driver(s) operate the Oldsmobile. What type of load is the Aurora subject, one person, two persons..? Is the car used to tow? If so what and how often?