XE282S in my 408??? Big enough or bigger?

Your rear gear ratio plays a big part in the stall speed of your converter. If you were to order a converter with a 3000rpm stall for 3.9 gears it would most likely be over 4000rpm with 3.23 gears. The recommendation from edge racing converters for that cam in my sons 410 with 2.92 gears was a 3000rpm stall it works really well. He stuck with 2.92 gears as the car spends quite a bit of time on the highway at 70mph for long distances. Based on his combo which is very similar to yours i would be thinking 3.23 or 3.55 gears depending on what you use the car for and a 3000rpm stall, custom built for those gears.