We just got a 1965 Mustang 289 from my fiance's uncle and it's time for some maintenance to be done. It's been in the family it's whole life too. It's completely original/stock with the stock 289 that has never been rebuilt. Her family thinks that the OD has rolled over so no idea how many miles it has on the car/engine. What are some recommended oils on a completely stock 289? Should I go to synthetic or would that risk causing possible leaks? Do I need an oil with high zinc (we do for our 76 MGB). 10w-30 vs 10w-40? I also need to replace the trans fluid and rear diff fluid too. Any recommendations on that?