How much marvel mystery oil do you add to my 67 bug?

For a 1967 Volkswagen Bug, it's generally recommended to add about 1 to 2 ounces of Marvel Mystery Oil per quart of engine oil during an oil change. You can mix it in with the oil to help improve lubrication and clean the engine. However, always refer to your owner's manual for specific recommendations and ensure not to exceed the manufacturer's guidelines.