The plug is located just to the driver's side of center, towards the front of the rear end (just behind where the drive shaft bolts up). If you are feeling around for it, you should be feeling for a plug that sits about flush and has a square cut-out for a 3/8" drive wrench.
As for the pony rims, I run 245/50/16 rear and 225/55/16 front. I think it's a nice stance, and I have no clearance issues. I could post a pic if you'd like.