Pinion shaft seal replacement

Ok, I need some help. 68 Dart GTS, 340. Can someone confirm correct torque spec. for pinion shaft nut? I think it is 230 ft. lbs., but not sure. Does it need to be torqued to this value, or can I follow some youtube videos where they mark the shaft & nut where they tighten the nut with an impact wrench the same number of turns and align the marks so it is back to original position. (Makes me a little nervous to do it this way without some input).

Also replacing the transmission rear seal at the same time.