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.
Buy the 3" mufflers and do the install when you get the 360 done. At least then you'll have them on hand.