Do I Need a Bushing for the TC for a 273/318 Swap?

Best thing would be to replace the TC when replacing the engine. Probably be better for the balance and maybe stall speed... Just a guess. Correct pilot bushing...
That's something that would have to be made. There weren't any factory torque converters with a large button that fit the early ('67 and older) 904's. I understand that you can also change the pump and input section of the transmission to do the conversion too, but, I've never done it that way myself.