opinions wanted please

Im going to carlisle next weekend and plan on picking up some mufflers. I want 3" mufflers along with 3" going right out the back. My issue is will this be fine with my sb 360 for now. I plan on doing the motor next year but until then it will be stock. I got a set of hedman headers on there right now but im worried if i go as big as 3" then i wont have enough backpressure! Just looking for advice fellas Id appreciate it.