B Body 904 Transmission int a 65 A Body

You will need a custom converter the bushing you are referring to is to put a small hub converter to a large hub crank and the 273 never had a large hub crank as it was dropped for 68 so a custom-made converter is your only option. Are you sure you have a 273 engine? Many a 273 have been replaced by a 318 back in the day.